Trezeguet is a good striker,guessing he'd play well alongside Drogba. He cost me 16M and 15% of next sale clause, so a little outside your price range :P
For a defensive midfielder i'd go with poulsen (can't remember his first name nor club; just search it and you'll find him) or tymoshuk (sp?) from zenit st petersburg, both cost around 10-12m.
Not sure about a keeper, you could try Ben Foster from Man Utd, not sure if they'd sell him to Chelsea and he's injured for most of the first season. After the 2nd season he's amazing though and might give Cech a run for his money.
Hope i helped :) | 
