Too many naysayers for .co right now. Start posting your domain name in game forums if you haven't already; someone will want it. Maybe not today, maybe not tomorrow... patience. The holder of the dot com version most likely wants too much for it, so the next best TLD for someone with a smaller budget is the dot co - which should be less expensive since it's still a pretty new extension. With a .co extension, best thing to do would be to build a site around it. Get a PageRank and some traffic, then try and put it up for sale.