- Prototype 18.104.22.168 - one of the originals, at least the first one I remember
- 94k uncompressed
- jQuery 1.1.2 - great, tons of examples, and documentation
- 54k and compressed to 24k
- MooTools.net 1.11 - awesome, tons of examples, and documentation.
- Core Only 4k and compressed to 3k
- Everything 87k and compressed to 43 k
- script.aculo.us 1.7.0 - requires 7 files plus an included version of prototype.js
- Adobe Spry - beta
I just seriously started reviewing these today but it seems jQuery and Mootools.net are stand outs. jQuery also has the advantage of Digg.com switching from script.aculo.us for their site.
I know this not a complete review and I will add more to the list as I learn about them.