well for mystery you can read all the nancy drew books
desperation by stephen king is really good.
The regulators is pretty good and is like a mirror of Desperation that he wrote under Richard Bachman.
SK's newer books are less horror and more thillerish
World War Z is great but is written in a wierd style. It about a zombie outbreak that almost eliminates the human population and about a reported who goes around and interviews people afterwards when the "war" is finished. The cool thing about the book is it's about a world wide happening and not like most movies, etc...that are confined to one town, one state, one country; the scope is much bigger.
Neil Gaiman's books. Neverwhere is amazing. It's like a modern day Alice in Wonderland, but a bit more macabre and with adult themes. The Anansi Boys is another good one by him. He also co-wrote a book with Terry Prachett (author of the Disc World comedy/fantasy series) called Good Omens that is one of my favorites. It's about armegeddon and an Angel and Demon that are loosely friends that are trying to stop the end of the world because they like it so much.
An entertaining classic, The Cat's Cradle, by Kurt Vonnegut. It's about a reporter tracking down and interviewing the kids of a famous scientist that supposedly invented this type of ice that stays frozen up to much higher temperatures and when it interacts with other water molecules, it "teaches" them it's genetic code and makes that water act the same.
George R. R. Martin has a high fantasy series that spans four books so far that's an really epic read. It doesn't involved very much, if any true magic and it's more about the intrigues of the court and all the backstabbing that goes on. There's battles and all that too, so it's definitely worth the read. No elves, hobbits, or anything too out of the oridinary here.
If you want more fanatasy, Raymond E. Feist has several sets of books that have the high fantasy with magic and demon races and all kinds of crazy stuff. Usually I can't start reading one until I have to whole set because there's cliff hangers and such that just keep you wanting more. Some of his books may seem a little repetetive but they have characters who's paths cross and some that are ageless that may play minor roles or something major in the novels. Very good stuff.
Terry Prachett that was mentioned above does fantasy humor. His stuff is great if you want a fun light hearted read. His "Disc World" is a flat disc shaped world that sits on the back of an elephant that stands on four giant turtles that float through space. He's british, so you have a lot of the typical british humor in his novels.
Often difficult to read, but well worth it if you're a fan of horror and suspense, Howard Phillips Lovecraft. Considered
the original horror writer, he created a character that inspires and touches the works of many, many authors, including some of those above. Call of Cthulu was considered his defining "book" in his carreer. Most of his books are short stories but there's some very very good stuff in there if you can get past the fact that the language is considered so weird since it was written in the 20's (iirc). His early stuff is a little weak, but if you read the material that he was writing later in his life and carreer, then you'll probably walk away satisfied.
Edit: We should keep this going as a general book thread. I read a lot and I'm always looking for reccomendations no matter the genre. I hate picking up a book off the shelf that sounds like it's going to be good and getting stuck fourty or fifty pages in because it's such a dry read.