I'm currently in the planning stages of starting out on my own* (with a business partner...) and am trying to come up with a list of minimum requirements that I'll need for the early stages of this venture.
Leaving out the business craft side of things (sales marketing etc.) at this point - there are plenty of articles here on SO covering that - and focusing on the technical side of things only, I have the following list:
development box (obviously! PC or MAC depending on target platform)
dev software (VStudio/eclipse/xcode/notepad)
test box (could be virtual machine)
Source control (anything except VSS!)
onsite backup (external HDD, separate backup box, CD/DVD ROM)
offsite backup(looking for suggestions here amazon S3?)
teleconferencing software (for discussion with Biz partner who may not be local. Skype?)
bug tracking/management (fogbugz?)
Have i missed anything and/or included too much? I realize that every venture is different, and technically, the bare minimum is just a dev box and a chair... however assuming serious work with disaster recovery is in order, is this list reasonable?
[EDIT] I've created a wiki summary of the answers. I've put the skeleton framework in and intend to fatten it up with links and details etc. Once I can, it will be the accepted answer, in the meantime please vote up the other answers and/or edit the wiki page if you think it's appropriate. BTW, I'm away for a few days so the fattening up will take place after that.