Ajax trimed down to the core : AHAH, which stands for Asychronous HTML and HTTP. Despites its uber stupid name (google something with "ahah" ? ahah, gazillions of irrelevant stuff) it's a neat 2 functions javascript file that is all you need for most of your AJAX needs. (a little example)
Instant Polaroid Effect to Your Pictures With Javascript
This is pure awesomeness. Instant.js is an 8.5 kb javascript file (uncompressed, you can shrink it down to around 5 kb) which adds on the fly a "Polaroid Effect" to your pictures (white frame, light curl and a drop shadow). What I like about this is the unobstrusiveness (?) and the fact it does not use Flash. Too bad MSIE…