Will Bower posted the following link on facebook tonight and I wanted to pass it along.
The four key GOP Senators who need to hear from us (try phone lines, try FAXes, try the email addresses we have listed) are: Senator Olympia Snowe (Maine), Senator Susan Collins (Maine), Senator George Voinovich (Ohio), and Senator Arlen Specter (Pennsylvania). All the contact information you need to reach these offices ASAP.
The page is a database of phone numbers, fax numbers, and emails for each Senator. They suggest you contact the two Senators from your state and then work through the rest of the list as well. In terms of effectiveness, phone calls and faxes are most important, followed by emails.