Waiting for the mods to come out will be the highlight of your purchase. Many are in the works. Two big ones that come to mind are
OSP (If you don't know what OSP is, go to the site and find out.) and
Doom3Fortress.
Sounds good to me. Plus it's good that doom3 is out now, gives me a springboard of hope that we'll see quake 4 in (maybe) 2005.