Javascript

For those of you working with Javascript, there are a couple tools you should get familiar with.

Install firebug (a firefox plugin). Yes, it has a debugger and you can set breakpoints with it.
Install the spket plugin for eclipse. This is the best Javascript IDE I have seen so far. It has code-completion, formatting, javadocs for javascript, etc. You must use eclipse 3.2 or greater. To install it, just download the archive and copy the files & folders in eclipse/plugins to your eclipse/plugins directory. Do the same for the features.
JSLint your javascript code. This helps with rogue commas, semi-colons, etc.

Please add the pertinent links and any other config steps you come across in the future.