Rey Mysterio - He'll be dressed as some sort of superhero; I'm going with Iron Man.
Triple H - I see him breaking out some new tights, especially if this is gonna be one (if not his ) last match(es). I see him wearing green tights with black lettering, as a tribute to his DX days.
Alberto Del Rio - For some reason I see Del Rio is all white. White tights and white boots...the whole nine yards.
The Miz - It's his first WrestleMania main event, so he'll totally be pulling out some new gear. We have seen him wear black, red, blue, and purple, so I'm going to say he'll be rocking white as well. White tights with blue designs/lettering.
Edge - He seems to always have new gear at Mania, so I don't think this year will be any different. I see him going with some sort of green and white camo.
CM Punk - I see him debuting new Yellow/Black tights, with the "After Shock" logo on the ass.
I see Mysterio as Captain America. I don't know why, I just bet he will. Either that or SOME kind of famous, instantly-recognisable character that's been talked about recently.
Triple H will wear the same as he always does. As will most people. I'd love to see Cena sporting something other than that horrific purple abomination, but knowing WWE they'll mess it up and he'll end up in something even worse. Like yellow.
Rey will have a funky superhero costume. But I think guys like Punk, Orton, Miz etc will just break out a new color on their trunks. I'd like to see Trips switch it up a little. The white boots he wore at Mania XX looked awesome. He'll most likely just have a different design on them though.