As per title it looks like Amazon are price matching Steam on the daily 2K deal, is a pretty good price, has only been cheaper on GetGamesGo once before.
Borderlands 1 GOTY is 14.99 also though this is less of a deal
Both games register on Steam
NOTE: You will need a valid US address on your account to purchase digital games from Amazon, personally I choose to stay at the Las Vegas Hilton when I buy games. It has been noted that you should pick an address in a state where Amazon do not charge Sales Tax list here
If you want you can use my affiliate links for the above. (You pay the same I get some of the money Amazon would normally pocket)or use someone else from OzBargains affiliate link from here