I have to agree with the Ender series. It's not overly heavy on sci-fi per say, but it's very well written and full of great interaction between all characters.
Can't think of anything else at the moment. I have this book, The Dreaming Void by Peter F. Hamilton sitting on my desk waiting to be read and I think it's a part of a trilogy. It looked interesting when I bought it (impulse buy really); so we'll see how that goes.