A lot of the big ones have already been mentiond, but another signing that could have quite a positive impact would be Randy Starks.
Doesn't miss games, quietly plays on a high level in either the 3-4 or 4-3, can get to the QB quite decently, while still having some nice size to him.
Going by position alone in the draft, I'd still like to get another OLB. You can never have enough pass rushers and, in my mind, three is the minimum of guys I'd want to have who can get to the QB.
Realistically, get rid of Finley and get someone at TE who can make something happen, but who can play that reliable security blanket type of TE, as well. Wouldn't mind seeing Eifert in green and gold, even though some might see it as just a bit of a reach.