My front seven Patriots 3-4 defensive board, going into the Combine:
NT - limited options, as usual
BJ Raji, BC
Ron Brace, BC
Sammie Lee Hill, Stillman
Terrance Taylor, Michigan
Chris Baker, Hampton (major character concerns)
DE - decent depth, but few elite options
Tyson Jackson, LSU
Jarron Gilbert, San Jose State
Fili Moala, USC
Ziggy Hood, Missouri
Alex Magee, Purdue
Dorrell Scott, Clemson
Demonte' Bolden, Tennessee
OLB - great options in #10-20, and decent second round depth, then tails off
Brian Orakpo, Texas
Aaron Curry, Wake Forest
Everette Brown, Florida State
Aaron Maybin, Penn State
Brian Cushing, USC (might project better to ILB)
Clint Sintim, Virginia
Larry English, Northern Illinois
Conner Barwin, Cincinnati
Paul Kruger, Utah
Clay Matthews, USC
ILB - thin after top two or three
Rey Maualuga, USC
James Laurinaitis, Ohio State
(Brian Cushing would be here)
Tyrone McKenzie, South Florida
Marcus Freeman, Ohio State
Scott McKillop, Pittsburgh
Darry Beckwith, LSU
Dannell Ellerbe, Georgia
Mortty Ivy, West Virginia
Note that this is not how many of these prospects are listed, but where I think their position falls in the Pats 3-4 system.
I don't think the Pats secondary is so different from other defenses that you need to adjust.
One secondary player not listed earlier I am intrigued with is S Michael Hamlin of Clemson, with 110 tackles, 10 PBU's and 6 INT's. I would look at him as a candidate for the late second pick - great productivity, although he may lack speed. Critical combine for him.
I listed all the players in each category, since there might be a higher first from a Cassel trade, or less likely a trade up.