I am the author of TradeSkillMaster (see my signature), which has become one of the most widely used addons for making gold off the auction house / professions in a relatively short amount of time (the Auctioning module was originally based on Quick Auctions 3). In a few weeks the amount of free time I will have to work on TSM will be significantly reduced due to RL stuff. I will still be working on it fairly regularly, but I'd like to see new features added at a faster pace than I alone will be able to. There is certainly no shortage of things to be done on this addon.
Keep in mind that this is a hobby and not a job so you really have to be motivated to contribute. I am looking for people who have a solid programming background (lua / wow addon background would be great). If you use this addons that's obviously a plus, but certainly not a requirement. While this is a volunteer project, I have been known to be generous with curse reward points 8).
If you are interested or have any questions, please contact me in IRC (tradeskillmaster.wikispaces.com/IRC).