Introduction to Linguistic Theory
Additional Materials on Articulatory Phonetics and IPA
Interactive Chart of IPA Symbols
Not only do these charts nicely describe and organize the IPA symbols, if you click on a symbol you'll hear the sound it represents!
Interactive Sagittal Section
Just click the buttons that describe the sound, and you'll get the IPA symbol that represents it, as well as a neat picture of how the phone is produced.
The Website of the International Phonetic Association
This has more information about the IPA, symbols, definitions, etc.