Cover in central defense with Carvalho off and Terry's injuries.
Cover for Cashley Cole definate.
Maybe a young midfielder with the potential to learn from Essien, Mikel, Ballack and Lampard.
Up front Ade and if you don't fall for that, a decent young striker.
The main thing is you need quality youngsters to bring new blood into the team.
To be honest two to three quality signings will only keep you at last seasons level, due to so many players beginning past their prime. Chelsea need closer to half a dozen quality recruits to challenge for the EPL.