Completely and totally guilty of this, as well.
Most recent example was a few weeks ago when TRU did the clearance. I only really wanted Virtua Tennis 3, and yet ended up coming home with Blue Dragon, Stranglehold, and EDF 2017. Now, that sort of worked out, because Stranglehold is about $15 worth of entertainment, no more, and EDF is one of the most awesome games ever.
Blue Dragon. I don't play RPGs. ESPECIALLY older or 'classic' styled ones. Closest thing I play to RPGs are the BioWare games. Hell, back in the day, I picked up FF7, played it for about 10 hours, hated it, and sold it off to my friend for $10. So, that all begs the question... why in the hell did I buy Blue Dragon? Answer: because it was cheap.
After that, I really have tried to limit myself to cheap games that I *want*, like Beautiful Katamari for $13, stuff that I've wanted and isn't easy to find a deal on, like Rock Band, and stuff that I'll get day one no questions asked, like Mario Kart Wii and GTA4. As of now, I've done pretty well. I've only picked up for games this week, all finally cheap enough to warrant a purchase.
Whether people want to believe it or not, it's an addiction.