Saeed Abedini is probably the most famous of the four imprisoned Americans. It's been three years of being repeatedly beaten in a brutal Iranian jail for him. He only went over to Iran to help with some local orphanages. Here's a video Saeed's wife made a few months ago, when Saeed missed yet another of his son's birthdays.
If you're in Colorado, like me, here's the links to write to your senators.
Email Senator Bennet: https://www.bennet.senate.gov/?p=contact
Email Senator Gardner: http://www.gardner.senate.gov/contact-cory/email-cory
If you live in a different state, you can go here to find your senators. (Just choose your state from the drop-down menu.) http://www.senate.gov/general/contact_information/senators_cfm.cfm