I like the eBay idea... cause if you sell/buy/trade with someone here, you know who you're dealing with. That could be pretty fun.
Also, a forum feature I always thought was pretty neato is the "karma/mod system" the Red vs Blue forums have. Here's an example of
what it looks like.
And this is the info about the mod system from their FAQ:
A: Karma is a rating system where your karma level is raised based on how much you use the site and how much positive feedback other users give you. You can gain karma for making comments that get modded up and you can lose karma for making comments that get modded down.
Q: What are mod points? How can I get mod points?
A: Mod points are ratings given to various posts around the site. You can gain mod points by using the site and making positive comments that get modded up.
Q: Can I trade all my mod points to my friend so that he can then trade mod points back to me?
A: No, if you do this we will see it and change your level to level -1 and take away all your mod points.
However, now that I think about it we already have the MGBux system... oh well ^_^;;