My install is:

- Web Developer
- User Agent Switcher
- Greasemonkey/Platypus
- Allow Right Click (now duplicated in FF but neither works)
- Google Toolbar + googlebar (for the right click options)
- Add N Edit Cookies (excellent tool)
- Live HTTP Headers
- Undo Close Tab (VERY useful, if you accidentally close a tab then right click, select and it will reopen it)
- Download Statusbar (undecided about this)

A last one is "Session Saver", however I only used this at work and 1.5b knocked it out. Basically it will preserve nearly everything you were doing in the browser and reopen it where you left off, presumably you can syncronise this across several machines if you want. It will even preserve it after a crash and even restores part-filled forms and text boxes.

Gareth