I think Manning is a Colt in 2012. Same with Luck.
Seattle i think have a pretty decent WR core, Rice and Baldwin are both capable of getting verticle and getting seperation, both are tough enough to go over the middle.
If Manning landed in Seatle, i think more than anything else, they'd need to invest to upgrade the line and then look at an athletic pass catching TE
I think the Jets are the most likely landing if he goes but im not sure that Manning will want to get involved in that locker room right now, it seems completely shambolic. They have their work cut out for them.
Washington are an interesting option but will a dwindling Manning really want to play little brother twice a year, who might have more rings than he does soon, in a division that hosts a resurgant Giants, and also yearly SB contenders in the Eagles and Cowboys?
No way to my mind, unless Manning is confident he can take the division with the skins, otherwise he risks damaging his legacy.