Pressuring Republican Senators?

Potential Republican Senate Allies?

I'd like to know who are the Republican Senators most likely to work with Democrats, those who might support or at least, not aggressively oppose Obama's agenda. Are there some, or are they all hardened ideologues? I'm interested in knowing what Republicans are most likely to vote across the isle in exceptionally close votes, and of course, any Senate Republicans who might be persuaded to shut down a filibuster led by their own party.

Also, in times past, we were taught that pressuring Senators in districts other than your own is not effective, and could actually backfire. However, in this age of instant internet fund-raising, is this still true? Can anything be gained by organizing efforts to pressure a senator from a part of the country other than where you live?

I'd love to read some discussion on this.