Psyringe: If 20 bucks are all that I can afford for the next 3 months, then I definitely wouldn't bet all that money on a single horse in any case. Instead, I'd choose 2-3 games from the genres I like most, and preferably ones that have huge modding support and a lot of user-made content. My preferred genres are strategy and RPG, so I'd go with either Morrowind GotY or Oblivion GotY, and Civ4 Ultimate. These are pretty cheap in the brick and mortar stores that still have them, so I may even have 5 bucks left to get a cheap shooter or racing game for even more variation.
macuahuitlgog: What brick and mortar stores are you talking about?
Here in Berlin, I've bought Civ4 Ultimate at MediaMarkt for 3 Euro . This was a Christmas sale, but they may still have it for 7 Euro or less. I think they also had Oblivion GotY lying around for either 5 or 10 Euro.
Usually digital distributors are cheaper than brick and mortar stores though - _if_ you are patient enough to wait until the games you want go on sale. However, there aren't that many great sales in this time of the year, just after the winter sales madness. If you don't want to wait, then the brick and mortar stores are worth a look.