My two favorites are Permutation City by Greg Egan and The Golden Age by John C. Wright (actually that one's a trilogy).

I hear good things about Iain M. Banks' Culture novels. I've only read one (The Player of Games) and while it was enjoyable it was still sort of meh, if that makes sense... (I've got Excession in my queue and I suspect I'll enjoy it more.)

While it's more in the realm of science-fantasy, you might enjoy this alternate universe imagining of the Harry Potter story: http://hpmor.com/