http://en.wikipedia.org/wiki/Green_Man_Gaming
It's legit. It's not a CD key generator site and it's been around since 2009. No problem with my purchase.
Links
http://www.getgamesgo.com/product/dirt-3
http://www.getgamesgo.com/product/total-war-shogun-2
I haven't made a purchase from this site, but these are the best deals yet on both games. Enjoy.