A few different places:
1. The weekly Book Reviews in the newspaper
2. Scanning fora like this one
3. Word of Mouth with friends - including a great librarian who is always in the know!
4. Book blogs and social networking sites devoted to books. The old Readerville site was a goldmine, I haven't found anything as good since it expired. I've been checking out GoodReads and Shelfari occasionally, but somehow I haven't connected with either of them in the same way. Honestly, I haven't joined any site yet, because I haven't figured out which one I should put my time and energy into....I'm debating between GoodReads and Librarything, and leaning toward GoodReads.
5. The library - I always check the "Best Bets" shelf and I often just scan the shelves for interesting looking reads.
6. Book awards - long lists, short lists and winners for awards. I like looking internationally, so I check out quite a few: the (U.K. based, but awarded to Commonwealth writers) Man Booker, the Orange, the Pulitzer, the (U.S.) National Book Awards, the Nobel, the Australian Miles Franklin, the Canadian Governor Generals and the Giller, etc. as well as a fair number of children's awards (Carnegie, Guardian, Costa/Whitbread, Newbery, Printz etc.) and a few genre awards (Hugo (science fiction), Dagger (crime), Edgars (crime) etc.). Those are just a few of the awards out there and they are a goldmine for good writing. There are similar lists for non-fiction, if that is your preference.
If you go to the award sites, they usually provide historic lists of nominees, and many go back 50 or more years, so there is always something to consider.
7. Booksellers - knowledgeable ones, at least. That usually means independents, but some large chains are better than others at hiring knowledgeable sales staff. If you are lucky enough to have a Kinokuniya nearby, I always found their staff to be very good.