Two and a half years into my bachelor's, Sipser's Introduction to the Theory of Computation is the only computer science textbook I've had so far that I'd say I really found useful for anything beyond the homework problems, besides K.N. King's C Programming: A Modern Approach.
(To keep this on topic, my assembly instructor -- the legendary [to NC State students] Dana Lasher -- posts his course pack online. [1] It's a comprehensive introduction to computer architecture topics and original 8086 assembly programming.)