My game consoles.
Seriously. They were 100% impulse buys, because it seemed "good at the time".
Sure they got lots of use initially, but being an FPS gamer, I gamed on the PC because (by comparison, and 100% IMO & IME - not wanting to start any system wars!!) console FPS sucks balls.
Being a PC player for longer than most console players have been alive also helps swing it for me.
My latest waste was a PS3 slim. Cracking console, but hasn't received the attention that it deserves from me - I'm still taken with playing FPS games, and PC gaming in general.
Anyway, my car would rate as a waste of money. I bought one month too early, and moneys was a bit tight. Made some silly financial decisions and will be dealing with the reprocussions for about 18 months more to come (car purchased early Jan 10). I could have waited a month, but nooo, I had to have it *NOW* and spend the banks money to obtain it. Large fuel bills and a Europe trip as well has left me rather short of £££ tbh.
By contrast, the EU trip itself was worth every p. Just wished I did it a little later.
Ho hum.