The ones that stand out are:
- Check my links - This is a good plug-in to check for the page you are on. Still I recommend downloading xenu to check the whole site.
- Firebug Lite - Nice plug-in light weight from toolbar.
- yslow - This is pretty much a standard tool to have in your arsonal as it provides reasons why your site is so slow
If you know of any others that are useful please email them to Susan Fischer at email@example.com and we will post them here.