Outside of that, I think the biggest gaming influence for me was actually Warhammer 40,000. The original book -- Rogue Trader -- was incredible. It was VAST, an entire universe, in far greater detail than was necessary to run a tabletop miniatures game. I loved that it was well defined but also left wide open. They detailed more than enough to play in the writers' world but left the rest of the universe (such as hundreds of space marine chapters) up to the players to flesh out. It was more RPG than wargame. The next 40K book, Chapter Approved, was also great. The art helped, too; it was a very unusual style. But I'd have to say that my #1 biggest influence was the first volume of Realms of Chaos (the one with the red cover). It was the weirdest, most wide-open, most beautiful game book I'd ever seen at the time (and still ranks up there). I think it was from those books that I got a taste for worlds that are really huge, kind of weird, well defined in some areas, and open for development in others.
Unfortunately, I sold my copy of Realms of Chaos on an internet auction when I needed some cash back in college. It went for $80, as I recall. One of these days, I'll buy myself another copy...
I have to agree on the Warhammer universe as a major creative influence. Rogue Trader is superb, especially the art. All of the pages of art plates and the fluff (the images of mercenary marines sitting in bars really set a wild mindset to the universe that I think they lost with the second edition when they went over the top with the dark, gothic atmosphere and got away from the wild, anything goes universe).
The first Realms of Chaos book, Slaves to the Darkness is a mindblower, hands down. The wide range of art, the weird chaos attributes and weapons. I sometimes grab my copy out to just to look at all the weird imagery. The second volume, The Lost and the Damned has a lot of Adrian Smith black and white art, which can be quite disturbing, but the overall feel is not as chaotic, if you will, as the first book. In the back of the Lost and the Damned there is a game called Chaos Warbands, a skirmish game, that GW has resurrected with the 6th edition of WFB. In college we spent countless hours playing the chaos warbands, it was incredibly and simply fun.