Best fits?
You have to discuss Adalius Thomas. He plays the Willie McGinest role in Baltimore's 3-4 - big OLB, sets the corner vs the run, rushes the passer. He would be huge here, in a rotation like the McGinest-Vrabel-Colvin group, or enabling Vrabel to stay inside.
Don't know if Antwaan Peek would be good in the OLB rotation. He has played in a 3-4.
Obviously Donnie Edwards would help on the inside.
I think Kevin Curtis would be one of the best fits at WR. Small but quick, gets open, and very fast, could stretch the field. He can also return punts, which would help.
There's not an experienced wily veteran to replace Vinnie Testaverde available out there. The Pats will need a third QB at some point.
It would be nice to have a real back-up center. The Cowboys have two centers in free agency, and presumably will focus on Al Johnson. I don't know much about Andre Gurode, but he could probably compete with Mrooch for the back-up C/G spot.
DB is complex. The Pats have four fairly good ones in Harrison, Wilson, Sanders, and Hawkins, plus Tebucky and Mitchell coming back from IR for special teams, and I assume they will use at least one of their day one draft picks on a safety. And if Samuel comes back, the Pats have Samuel, Hobbs, Gay, and Scott, plus Spann or special teams and another of the day one picks, if things fall right. So bringing in a DB is tricky.