Well, if you have LOTS of time, our player models need changes. Like, all new animations (the existing ones are really bad), or some optimizations (they use too many polygons for their quality). But it's been that way since 1.0, so this isn't urgent, but you'll get LOTS of fans if you succeed.
Personally, I'd like something simpler for a start. Can you make a model for the "gravity bomb" and the "Port-O-Launch" projectile?
Gravity bomb: heavy looking, preferably black, large, either boxy or spherical thing. It is always fired by dropping it straight downwards, it never moves in another direction.
Port-O-Launch projectile: preferably glowing ellipsoid-y projectile, would be nice to have rings on it. With some neon color, the rings could be black or white.
If you have more time, I can look for all "recycled" models in Nexuiz, and tell you which should be replaced

1. Open Notepad
2. Paste: ÿþMSMSMS
3. Save
4. Open the file in Notepad again
You can vary the number of "MS", so you can clearly see it's MS which is causing it.