If you can only buy two javascript books…
they should be JavaScript: The Definitive Guide by David Flanagan, and Ajax Design Patterns by Michael Mahemoff.
The former is like an encyclopedia for javascript. It has almost everything, even the meanest, baddest codes (I meant it in a good way). A good reference book. For anyone who has been coding for a significant while, you probably already realize that coding is usually the easier part. Design pattern is the tricky one, however. A good pattern design goes a long way. That’s where Michael Mahemoff’s book comes in. Some of my favorite methods include submission throttling, prefetch ajax and Guesstimate.
