The Vendel Mastiffs are awesome, they produce 12 in total two sets of 5 one with and one without a collar and then one sitting and one lying down.
http://picasaweb.google.co.uk/TheFeatheredSerpentProject/TheFinalStagesFallOfTenochtitlan/photo#5085280854212065170Reaper also produce a fantasy pack Packmaster and hounds which has 2 Dobermans and 2 Alsatians (which if you cut off the tails look like dobermans)
Obelisk produce a Doberman and a Rottweiler in their Gangstars packs which are lovely models, you might be able to buy these separately.
Mordheim had some fantasy rotweillers some time ago which were brutish looking, eye patches, chains and spikes.
The LOTR are quite small but nice also possibly worth looking at are the GB Wolfhounds, Eureka Wolfhounds (again small - in the conquistadors range) and the Ooutpost wolk hounds - nice and big good dynamic poses.
Megaminis have their Fox and hounds which look pretty good too