We need:
RB: We've been linked with Bosingwa and Daniel Alves, but I'm hoping we snap up Rafinha who, for me, is a better defender than either and can get forward just as well. Because he plays in the unfashionable German Bundesliga he'll no doubt be cheaper than the more fashionable Portuguese and Spanish players.
LB: Could do with cover for Evra, or even a player to replace him if he goes. I can't really think of any top LB's though, the best choice for me would probably be Urby Emanuelson of Ajax who looks like he can whip in a mean cross, but I've only seen him on Goalissimo

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ST: Been linked with everyone here, personally I think we need 2 as we only have 2 at the moment (Saha doesn't count and will go), so Huntelaar and Fabiano would allow us different styles, both are more forward players than we have and both can head the ball. Depends if you want a more dynamic side or a more structured side.
I would hazard around £35-£45m to be spend in the summer on players, we're at a position now where we are on the cusp of something special and we need to spend big to fill that little piece of the jigsaw left.