The Federal Bike Commuter Benefit program allows $20/month through your employer, if they decide to opt into the program. Here's a little bit of info on the program:
http://www.sfbike.org/?commute
http://en.wikipedia.org/wiki/Employe..._United_States
My company hasn't opted to participate in this, as it seems that the overhead to manage this for only a small handful of commuters is something they don't want to deal with. I'm hoping they change their minds at some point...