I've had some good suggestions for the FreeDevelopmentTools list, have added a few things I've thought of myself since, and most importantly have completed all the links.

There must plenty more out there, though, so keep the suggestions rolling in.

As I've already got a Troubleshooting tools list, I though next up should probably be an "invaluable utilities" one, but that will have to wait a while (but Scott Hanselman, amongst others, has already done a pretty good job for tools, add-ins, and "must have" tablet PC software).