I think a few people on here use this: http://www.squareup.com/
Been using square up for MONTHS and love it. Automatically dumps into your bank account, free card reader, no setup fee, no monthly fee. AND they just lowered their rate to 2.75% to accept any card with no additional fees...
AWESOME for mobile installs. I swipe it right after I'm done and off I go. Money in the bank.