I've seen lists floating around, but I've condensed this list, of Senators who are not clearly for or against a robust public option, down to a short cheatsheet that you can email, post, or print out and carry around.
Not sure - probably yes
Sen Robert Byrd (D WV) 202-224-3954 http://byrd.senate.gov (sick)
Sen Ron Wyden (D OR) 202-224-5244 http://wyden.senate.gov (yes)
Sen Dianne Feinstein (D CA) 202-224-3841 http://feinstein.senate.gov (yes)
Amy Klobuchar (D MN) 202-224-3244 http://klobuchar.senate.gov
Herb Kohl (D WI) 202-224-5653 http://kohl.senate.gov
Tim Johnson (D SD) 202-224-5842 http://johnson.senate.gov
Sen Michael Bennet D CO 202-224-5852 http://bennet.senate.gov (yes)
Not sure - probably no
Sen Kent Conrad (D ND) 202-224-2043 http://conrad.senate.gov
Sen E. Ben Nelson (D NE) 202-224-6551 http://bennelson.senate.gov
Sen Evan Bayh (D IN) 202-224-5623 http://bayh.senate.gov
Sen Thomas Carper (D DE) 202-224-2441 http://carper.senate.gov
Sen Mark Warner (D VA) 202-224-2023 http://warner.senate.gov
Olympia Snowe (R - ME) 202-224-5344 http://snowe.senate.gov
Mary Landrieu (D LA) 202-224-5824 http://landrieu.senate.gov
Johnny Isakson (R GA) 202-224-3643 http://isakson.senate.gov
Joe Lieberman (I CT) 202-224-4041 http://lieberman.senate.gov (no)
Susan Collins (R ME) 202-224-2523 http://collins.senate.gov (no)
Swing votes
Sen Blanche Lincoln D AR 202-224-4843 http://lincoln.senate.gov
Sen Mark Pryor D AR 202-224-2353 http://pryor.senate.gov
Sen Mark Begich D AK 202-224-3004 http://begich.senate.gov
Sen Jon Tester D MT 202-224-2644 http://tester.senate.gov/
Sen Max Baucus D MT 202-224-2651 http://baucus.senate.gov
Sen Bill Nelson D FL 202-224-5274 http://billnelson.senate.gov
Names in bold are Senate Finance Committee.
Let me know if there are any errors or updates.
Sample zipcodes: 99506 Anchorage AK, 20151 Fairfax VA, 33128 Miami FL, 04576 Southport ME, 72201 Little Rock AR, 59601 Helena MT, 46201 Indianapolis IN, 70112 New Orleans LA, 68901 Hastings NE, 06101 Hartford CT, 58282 Walhalla ND, 30301 Atlanta GA, 55801 Duluth MN, 57401 Aberdeen SD, 53201 Milwaukee WI, 25813 Beaver WV