Last week, i started a project, which needs a lot of javascript, Ajax. at the first i decided to use small javascript libraries for enabling ajax in my pages. But then, i remembered that there is a complete javascript library named ProtoType, i downloaded the documentation and noticed that there is a powerful class named ajax in this library. it was fantastic. Also there is an effect library, using prototype, named scriptaculous, it provides easy-to-use effect classes with a very light weight. I Recommend downloading both.
Also there is a really nifty documentation for Prototype here.
I really love Ajax.request and Ajax.responders methods in prototype. they are so useful.

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Also Here is a generator for Ajax loading gifs (Ajax loading indicators), they’re really, really beautiful. Check it out…

Dr.Devil