Temeraire series by Naomi Novik
Gaunts Ghosts series by Dan Abnett (If you only read one, Necropolis. Still his best book to date and one of the only books on my bookshelf thats falling apart from use)
Anita Blake series (up to about book 7) by someone or other. Worth reading for the start of the series, as it's petty interesting, brings new stuff to the supernatural world, and has a complex main character. Unfortunately, as it progresses, the protagonist gets more and more unlikeable, more of a MarySue and the sexual tension that makes some of the story interesting just becomes flat out having sex with anything that moves and is in someway supernatural. It just turns into wish-fulfillment porn. Don't bother reading any more of the books, the series never recovers. After a while the books can top out at around 450 pages, with 20 pages of plot and story development, 5 pages describing her guns, 2 pages for the deus ex machina and 423 pages of various sex. Yes, that may sound tittilating, but it gets boring and pretty damn creepy at times. You end up flicking through the sex scenes to try to find some story.
A Brief History of Time by Steven Hawkings. Everyone needs to read this.
Discworld, by Terry Pratchett. No description needed. Read it.
Hitchhikers Guide, Douglas Adams. Sarts good, gets a little weak towards the end of the series.
Crystal Singer Chronicles (Killashandra) by Anne McCaffrey. Decent take on sci-fi with some nice twists.
Ciaphas Cain - Sandy Mitchell. The series is up to about 7 books now and is a must for anyone who likes sci-fi. He takes the grim darkness of the Warhammer 40k universe and adds a Terry Pratchett twist to it. Absolutely fantastic, funny as hell and packed with references to everything from cricket to aliens to Winnie the Pooh. Masterpieces, and one of the few series that pisses off the typesetters for the Black Library because of all the footnotes.