here. Go to redbox choose "rent with promo code" and enter code 42HY4V8E. This code is good until 04/18/10 for one free rental.
Also if you have never used redbox before there are a few promo codes that can be used. You can use DVDONME, BREAKROOM or DVDATWAG (valid only at Walgreens). These codes work one per debit/credit card. Also DVDKROG worked for me two days ago at Kroger it is also one per debit card and should work at Kroger and all its affliate stores. Go here for redbox locations.