As I sit here working through the todo list for my site redesign, I'm mostly down to bug-fixing - there's a few bits of stuff to generate, a couple tiny bits of code I might like to add to the backend, some stuff I may delve into S2 for. I really wish Livejournal had regex available in S2 instead of having to use homebrew, interpreted search-and-replace hacks...
I've been using the handy
Web Developer Extension for Mozilla for a while. It's a little on the sluggish side. But some Javascript debugging issues led me to
Firebug, which... wow. It kicks the Web Dev extension's ass.
Also, I think I have found something that will obliviate any desire to install Windows as a life-support system for IE when I get around to getting an Intel Mac:
IEs4Linux. WINE and some other hackery becomes an IE testbed. It seems to even make the process of having multiple versions of IE available for testing easy; I know this is a big hassle on actual Windows installs!