For sponsor you should take a look at
www.rewardthem.com
As for the domain, If the one you'r using allready get some good return trafic i'd stick with that.. Though the others are short they really don't have any ring to them imo. so your long url will propably be easier to remember than the short ones..
of the short url's i like 8mp.com the best, but if i was to type it in to return to the site i think i'd be typing 8pm.com instead, so If you do wan't to use one of the short url's i'd go with ss15.com