I just read What Program(s) do You Use for Web Development? so I thought I would answer here instead of just as a comment.
I use all of these applications/plug-ins on MacOSX.
- Jetbrains IntelliJ Idea. The best IDE I've ever used.
- Textmate. The best text editor I've ever used.
- DBVisualizer. Makes working with databases easy.
- Fireworks, now from Adobe and likely to vanish someday.
- Interarchy. For moving stuff from one system to another.
- Path Finder. It's not a development tool but a Finder replacement; lots of neat programming assistant features.
- Web Developer Toolbar. Although there is some overlap with Firebug, it's mostly complementary.
OK, you can argue with me, but these are my weapons of choice. MacOSX is of course also my choice, when I get one.