Arlen Specter (R-PA) chairs the Senate Judiciary Committee, likely an early battleground, and is generally considered a moderate Republican (unlike the junior senator from Pennsylvania, Rick Santorum, who I'd expect you can write off.)

Specter had to make promises about treating Bush's nominees "fairly" when hardliners tried to block his chair appointment right after the elections, but moderation is much more in favor now and Specter's historically been the pragmatic (some might say "opportunistic") survivor rather than an idealogue.