I just finished Anathem by Neal Stephenson, which I thoroughly enjoyed. It was the kind of thing I both have a hard time putting down, and don't want to be over when I'm done. I've stayed up a bit too late reading for a few nights so now I'm not as sleepy as I should be at this hour.
burntsolace:
I have been looking for a book suggestion for a while and that sounds like a good one. I liked Big U and Snow Crash but was not such a fan of Cryptonomicon.