Apart from the version control system (CVS/Subversion), you'll need something to register and follow up the issues (read: bugs) with your software. There are many great projects that will help you with that. Here is my short list:

• Bugzilla - Probably the most well famous system for following up bugs. It is huge and has many options. But it is designed specifically for developers. It might be a little overhead for 2-men show, though.
• RT - Request Tracker is another system, which is less developer oriented, but is still an excellent piece of software. Very clean design and a lot of flexibility. Practically bug-free too. :)
• Mantis - good, but somewhat "green". It is still in heavy development, but has the potential.

My recommendation is RT. But you don't have to follow, since there are plenty of alternatives out there. Just grab the one you feel like will do the job and enjoy your development cycle.

Leonid Mamtchenkov aka TVSET