I voted Mayweather - Cotto
Mayweather - Mosley
and Taylor Pavlik

Mayweather - Cotto because I want to see how PBF deals with someone who applies constant, effective pressure, and Cotto's probably the best in the game at that. I think Mayweather would probably UD Cotto comfortably and I wouldn't be overly surprised to see PBF TKO Cotto.
Mayweather - Mosley because I want to see Floyd keep on fighting, and Mosley (or Cotto) is probably the biggest threat to Floyd right now. Again, I think Floyd would UD SSM without too much difficulty, but Mosley has power and speed and that is what would make this interesting.
Taylor - Pavlik because I want to see Taylor fight the best in his division as opposed to blown up welters and jr middles. Ever since he got a gift against Winky (and maybe even Spinks, who knows I was hypnotized by boredom watching that fight and I have no idea who actually won) I've been waiting for someone to beat JT, I don't think Pavlik will beat him, but with Pavlik's style it'll be a fun one to watch.
I want to see all of those fights however.