Don't know what rules you decided on, but if i can put my Two cents in I would suggest as follows:
1) All Things Zombie: Better Dead Then Zed (plus the Haven and I, Zombie Scenario/expansion books)- The chain reaction system that ATZ uses is a very flexible system allowing you to tailor your games how you want, and with the challenge system in the rules you can easily incorporate an action not covered by the rules. Want your character to build a "distraction/Trap" for the zombies, then take a challenge test to see if you succeed or if you fail, Pass with at least 2d6 then the action goes off flawlessly, pass with 1d6 1st time then you made a mistake, but didn't fail so you can try again, 2nd time you fail, pass 0d6 then you fail outright. With a failure it could be as simple as the item, repair, construction, etc... not working, holding together, etc... or it could be as serious as the trap blowing up in your face or the "distraction" going off and attracting all the zeds to your location. Another nice thing about ATZ is that you can incorporate the rules from any other THW game that uses the Chain reaction system, so if you wanted to do a WWII scenario with zombies then use the NUTS! rules with the ATZ zombie rules, want some new Attributes for ATZ then draw then from Nuts!, FNG, or 5150. Want in addition to Zombies some Aliens then use 5150 with ATZ. Yes it can get bogged down if you have a bunch of players and zombies on the board. Word of warning though many find that the Chain Reaction rule system has a higher learning curve then most other rules, partially due to the fact that rolling a low score doesn't always mean failure, in most cases whey you are rolling a test vs your rep you want to roll as low as possible. Over all a great customizable rule system with great customer support on the THW Yahoo Group. You do have to purchase these rules, unlike the next two rules I am going to suggest. Also THW does have a proposed Post Apocalypse rule set, After the Horsemen, coming out soon (Ed the THW guy said baring any delays it should be released right around April)
2) Akulas AR:SE- a quick little rule set only consisting of a few pages, less of a learning curve to learn, also great for larger groups such as conventions. Free on one of Akulas Blogs
http://akulasrules.blogspot.com/3) Dead Walk Again- Another nice little rule system, the current version is a lot cleaner then the 1st edition. I will admit I haven't played the newest edition of the rules so I can quite comment on them. Free through the Dead Walk Again Yahoo Group
http://games.groups.yahoo.com/group/deadwalkagain/There are more rule sets out there such as Ambush Z, 7TV- 7ombie, No More Room In Hell, etc... I have played a game or two of many of these rule sets but I keep gravitating back to ATZ due to the great customer support Ed has, and the ability to tailor the rules as needed via Challenge Tests and the use of other Chain Reaction based rules.
As for terrain (any price mentioned is in US Dollars)
1) World Works Games- Great scenery that you print out and assembly yourself. I have the older Urban Mayhem sets and not the newer TLX sets, if you check out Vampifans blog (link given in a previous post) you can see how the WWG Urban Mayhem stuff looks since he uses that for a majority of his scenery. One nice thing with WWG terrain you can either have the buildings with a full interior or just as shells, and use the THW Building rules as mentioned above (found in I, Zombie and as a free download on the THW website) if they are shells. Also now available through WWG is some of the Ebbles Miniatures cardstock models through the Ebbles Lab section of the WWG site. The Resistance, Patrol and Convoy sets are great Military style vehicles that scale well with 28mm minis, plus they are cheap at $2.50 a set and you can print off as many as you need, so if one gets destroyed its not a big deal. If you want a Vault style play area there's also Guncrawl a Space Hulk-esque gme from Ebbles Miniatures/Ebbles Lab. The Ebbles Lab version included the Prop sets that Ebbles Miniatures had available separately, these include a Store room, Workshop and Barracks (along with a lavatory prop set). I use the Ebbles Miniatures/Ebbles Labs Prop sets to populate some of my Buildings like the Ebbles Miniatures Folding Unit Structures (which are currently unavailable), primarily the Barracks prop set for the bunks (single and doubles), desks, tables and chairs for Military barracks/Relief Station housing. The Workshop and storeroom props are used to populate a workshop building and a storage building. Cardstock terrain is a great inexpensive way to populate your table with scenery, and if it gets ruined its easy enough to replace, only down side may be the cost of ink for your printer and the time spent cutting and gluing.
2) Model Railroad Buildings- For 28mm you can easily use O-Scale model railroad building such as the Bachman Plasticville line. You can typically get the buildings either prebuilt or as kits. The downside is that most these will require some additional work to get them to look good, you will want to paint these and weather them to get rid of the plastic look, some you may also want to add a small amount of interior props such as the Grocery Store, since it has the large window front (I believe some of these may come with an insert picture for an interior, but I may be wrong). You could either leave the model railroad buildings as shells and use the THW Building Interior Rules, or you can furnish the interiors with props. Advantage- sturdier then cardstock and will last longer. Disadvantage- Cost, you are looking at say $15 for one building kit and even more for the prebuilts), you also will need paints, weathering chalks, etc... to get the buildings to look good. Time wise it could be less time then with cardstock modeling or it could be more time depending on how in-depth you want to get on how the buildings look.
3) Scratchbuilt- You build the buildings and other bits of scenery out of foamcore, bits, styrene sheeting, cardboard, etc... For this you could also use parts of Model Railroad buildings (say the face of the building) or even textures from cardstock models like WWG.
4) Props- Granted props can be found in cardstock models from WWG and other companies or even model railroad scenery. I believe this should be its own separate category though. Buildings are what makes the board look good in a zombie game, but props are what brings it to life. You can as mentioned go the cardstock route to model railroad scenery or even props manufactured by gaming companies. I would also included vehicles in this category, World Works Games have some nice models in their sets along with the Ebbles Lab vehicles or you could go the Die-cast and plastic model route (roughly 1:42 to 1:48th scale looks good, plus the Hot Wheels Motorcycles {the ones that are packaged the same as the cars} are close to scale too, if you can find them).
I myself have a mix of cardstock vehicles and diecast vehicles that I use along with a mix of cardstock and model (both model kits and model railroad) props that I use for my games. In addition to the cardstock buildings I have I am also planning on using some Model railroad buildings (such as the Bachman Plasticville Motel kit and trailer park kit) to populate parts of my board. For the railroad buildings I plan on getting a couple of the Trailer Park kits (three trailers per kit, two per prebuilt iirc) and maybe one of the Cape Cod Cottage kits to make a trailer park for my table (the Cottage will be used as the parks office), especially since I have yet to find a cardstock trailer that I like.
The nice thing about building the Zombie table is you can also use it for Post Apocalypse games (especially if you model some of the buildings and/or vehicles as ruins and wrecks). Plus for Zombies you don't have to have the game set strictly in a city, you could do a small rural town with a couple businesses (say a diner, a small general/grocery store, a farm supply store, post office, city hall/police station) and one or two housed in town with a farm on the tables edge outside of town with a wooded lot in between the town and the farm (great for limited LOS) or even have the entire game take place on a farm ala Night of the Living Dead. If you wanted to game a Dawn of the Dead setting you can do that too, either scratch build your own mall or use the WWG Mayhem Mall set. Or if you wanted you could have the game take place in an underground facility ala Day of the Dead (original 1985 version) or Resident Evil the movie (using the Guncrawl game tiles or even the Firstlight and Firstlight Retrofit {or the newer TLX sets Codename Titan and Titan Control} sets from WWG, and for a Day of the Dead setting you could also incorporate the WWG set Caveworks). The possibilities are endless.
While it may look like I am trying to push you towards the WWG cardstock models I am not, I am using them as an example of whats out there, you also have Fat Dragon Games and Mirco Tactix that do modern cardstock buildings. I only have a couple buildings from Micro Tactix, where as I have most of the older Urban Mayhem sets from WWG (only missing that I know of Mayhem Junkyard and Urban Grind, along with the multi-genre sets Cathedrea Noctis and Wild Woods Grove that I can use for a Modern Day zombie game), and I love the look of the WWG sets.