DrunkonDuty said:
Agreed. The inspiration that an RPG gives you is an important part of it. Of course one can get one's inspiration from ANY game or literature. Me, I like stealing from everywhere. Hence my love of GURPS source books.
Some of my old 3e favorites (many of which are now available at $10 each);
GURPS Cabal: Like the World of Darkness... but with less angsting about being monsters or ruthless mages! The setting works better for different types of monsters/mystics working together as well...
GURPS Creatures of the Night: Some
really disturbing monsters here. The author wrote them up after various nightmares he's had, and it shows.
GURPS Horror:
The definite treatment of the horror genre for role-playing games... at least, until they create a new edition for 4E.

GURPS Technomancer: Fun modern-day Alternate Earth where magic returned to the world in 1945. It has a somewhat unfortunate US-centrism, however...
Transhuman Space: The definite proof that "hard SF" doesn't have to mean "boring" - and reminds us that our own future might be stranger than anything we can imagine...
GURPS War Against The Cthorr: One of the best "alien invasion" scenarios I have seen - and one that doesn't even have any active
intelligent aliens that anyone has seen. For a really disturbing and depressing alien invasion, accept no substitutes.
GURPS Warehouse 23: It's not just the Ark of the Covenant that's hidden in there...
Suppressed Transmission 1&2: Not GURPS books themselves, but still very, very inspirational. Weirdness at its best.