Municipoll for PoliticsPA (PDF) (2/21-23, likely voters, no trendlines):
Bob Casey Jr. (D-inc): 50
Rick Santorum (R): 38
Undecided: 12
Bob Casey Jr. (D-inc): 51
Charlie Dent (R): 32
Undecided: 17
Bob Casey Jr. (D-inc): 48
Jim Gerlach (R): 34
Undecided: 17
(MoE: ±3.8%)
Bob Casey Jr. is one of the Democrats' lesser worries for 2012, according to one more poll, this one from IVR-based-pollster Municipoll on behalf of news site PoliticsPA. The numbers are quite similar to the Quinnipiac poll a few weeks ago, with Casey sporting a 46/30 favorable here, and leading potential opponents by margins ranging from 12 to 19. (Qpac had him at 44/24 and leading Generic Republican by 10, which is consistent with G.R. usually overperforming specific names by a few points.) Bear in mind that none of these three Republicans seem likely to run... in fact, after a flurry of speculation about potential GOPers in December, I haven't heard anything in many weeks about who might step up.
If for some reason Rick Santorum gave up his long-shot presidential bid, he'd still find himself pretty unwelcome for a return to the Keystone State, with 39/44 favorables; Charlie Dent and Jim Gerlach's problem, by contrast, is name rec (they're at 12/16 and 13/14 respectively). Newly elected GOPers Tom Corbett and Pat Toomey are still enjoying their honeymoons, at 48/31 and 42/35 respectively.