Half way into 2010, I realized there's probably a ton of unused codes that I've sent off to readers. You'd be amazed at how many people enter Dtoid contests and then never check their e-mails to claim the prize that they win, thus someone else scores the freebies. Moral of that story: Make sure you use an email you check regularly and that you actually check your email.
Back to the point, here's a ton of codes that may or may not have already been claimed. Do everyone a favor and leave a comment letting us know what codes are good or not. <3