I wouldn't say regret, because it as free, but my Dad bought me Aliens:CM on PS3 because it was £5. I said thank you and then wondered if he would notice if I never played it :/
To top it off he bought another copy on 360 for the same price so that he could play it :)
Also some shitty Euro 2008 football game I think on DS that I got when I was about 12. It looked absolutely awful, had no music and some of the blockiest 3D graphics I've ever seen (I have genuinely seen Mode 7 SNES games that looked better to my eyes)