The Dragon book is probably the best introductory text. The new version that came out a few years ago actually did improve the original text a fair bit. Although there is a lack of discussion about SSA in the text.
While most compiler books spend most of the text talking about the front-end of the compiler the crazy interesting stuff is in the backend. The new Dragon book greatly improves here over the old one, but I'd also recommend two other texts:
1) Morgan, Building an Optimizing Compiler -- some people love the writing style. Others hate it, but the material is solid.
2) Muchnick, Advanced Compiler Design and Implementation -- Great book. Must read if you're serious about optimizations.
Computer Architecture: A Quantitative Approach, 4th Edition by Hennessy and Patterson.
the Patterson and Hennessy is a good book to start with, too.
My knowledge is way out of date, but I think even back in 2000 those books were a bit behind the times in terms of optimizations production compilers do. For instance, there was little in-depth treatment of hot-cold optimizations in the 2nd edition.
The tension between processor architects and compiler writers is a constant theme.