I'm going to get some stick for this but I'd have Walcott.
He's got one year left on his contract at Arsenal so wouldn't cost too much and he'd be one extra not only for the Premier League home-grown rules but the Champions League ones too (I think these are slightly different?).
His pace is ridiculous and we've seen over the past two years how well Mancini and his team can improve the technical side of a player's game so I think he'd be worth looking at. I think he's wasted out on the wing but if you improved his finishing a bit (wouldn't have to be too much, crossing is his main flaw, he can finish, just doesn't do it consistently enough) then playing on the shoulder of the last defender he'd be lethal.
People will say he's not suited to our style of play but we saw this season how the short-passing, patient build up style can be stopped on occasion (Barca vs Chelsea and a few of our games) and so sometimes you need something a bit different.