Visible Vote Mobile (free) is a polling application that gives you insight to how your legislators are voting on bills. You start by entering your email, zip code and state, the application identifies your Senators and Congress person(s), then you "vote now" by basically reading through the unanswered issues - simplified versions of complex bills that are topical in nature, such as the "Credit Cardholders Bill of Rights", vote yes or no. A vote summary screen provides a "percent agree" with your specific legislators.
From within Visible Vote Mobile you can send an email to your legislators choosing one specifically or multiple. The makers of Visible Vote claim to send a weekly synopsis of the information they have collected from their users to the legislators.
In addition to the iPhone application there is also a Visible Vote application for Facebook.
Personally, I find the iPhone application adequate, the "Issues" are summarized accurately for the lay person, if you require more information, jump on the internet and dig into the proposed bill. One thing I have found, the bills of today are so broad, voting yes or no is difficult as you are often conflicting with prior votes.
Overall, Visible Vote keeps you informed of important legislation, gives you insight into how your legislators are voting and gives you a preliminary tool to take part in the democratic process. Not a bad start!