LB? While the Pats could use better mid-level quality behind Vrabel, Bruschi, and Colvin, they have lots of players on the roster that can compete - Beisel, Alexander, Claridge, Mincey, Tully Banta-Cain.
WR? It would be nice to see an experienced fifth WR, but it's also possible the Pats might just go with four, plus the three TE's and a pass-oriented H-back. Any fifth WR must have ST skills, either a bigger Bannister-like guy (Chas Gessner again?) or a smaller PR guy.
QB. Now here's where the Pats really need to make a move. Cassel shows some raw talent, but the guy just hasn't played much. Remember that he threw his first TD since high school in the meaningless Miami game. And behind him are two raw inaccurate udfa's. If Brady goes down for a couple games, this position could really impact the team. Look again at Tampa Bay, with Simms, Fiedler, McCown, Rattay, and some raw players. Fielder, McCown, and Rattay are all generally similar back-up players, and there's little point in keeping three midlevel back-ups. A deal for Rattay would make sense.