I think most of the manufacturers have been mentioned.
Pendraken, Kallistra and Magister Militum have the biggest ranges. Some of Kallistras stuff is based on Pendraken figures, but in strips and often slightly converted, but they also have a lot their own stuff too.
Eureka in Austrailia have some good stuff, but often more as a complement to other ranges.
Copplestone are some of the nicest figures, but they don't have too many packs.
The GW Warmaster stuff is genrally good, the more common stuff, Empire, Elves, Undead tends to go for an OK price. The BoFA plastics are mixed, the good guys are nice. The goblin foot are fine if a little regimented the wolf riders less so. The metals are very nice but very hard to get hold of.
It can be well worth looking at 15mm ranges too, Splintered Light in the USA have some very nice figures, I've used their Tree Trolls, Dryads and armoured Ogres with my 10mm figures and all fit in well.
Old Glory are worth a look, but I think they only do historicals.