Here are a few of the tools I find indispensable on a day to day basis.
Editor - Sublime Text 2
Two features here make it my #1 choice. The first is the ability to have multiple text insertion points. It's hard to explain, but just go watch the little video on their website. It saves a lot of tedius typing.
The second is the best file-find&open mechanism I've seen. When your developing a django site, you end up with a lot of similarly named files (views.py, urls.py, etc.) Sublime is the only editor I've found that lets me easily find the right one. A simple cmd-P to open the text box. Then a few letters of the app, a few letters of the filename, and it's usually got it. Example:
cmd-p pro vie ENTER
That would open up apps/projects/views.py in the current project I'm working on.
SQL Browser - Sequel Pro
The best SQL tool I've found.
Bonus points: It can connect to a remote server over SSH and tunnel the mysql connection over that, so you don't have to expose your DB to the internet for any reason.
Music - Spotify
How can you code without some music? Spotify has replaced the iTunes & Pandora that I used to use.
Screenshots - Skitch
The ability to quickly take, annotate, and share screenshots makes my life a lot easier.
Password management - 1Password
1Password lets me have a unique, strong password for every site that I sign up for.
Browser - Google Chrome
The developer tools in Chrome are the best I've seen. Superior to FireBug, and very similar to Safari's tools. (If you're debugging in IE, you're doing it wrong.)
Communication - GMail / GChat, Skype & Adium
It felt weird not to include these since I spend so much time in them.