Dokusai: I just chose games I enjoyed playing. That meant spending a little more money than I originally planned on, but it was probably worth it.
misfire200: I chose games that I felt were pretty darn good or since there are so many sales, I bought the most bang for the buck for my person. Obviously if they put them on there list, then any of the games they would want, but I also made sure to get them the most for the value and give them plenty hours of fun.
Bought my giftee four games total. 'Tis the season of giving, after all. ;) Three of them I know from my own experience are very good, and the fourth is very highly regarded so I doubt I messed up there. In addition I tried going for a different genre for each as not to make everything feel samey: an action-adventure, a point'n'click adventure, an FPS, and an RTS.