I've had too many ridiculous, random retail deals over the years, but here's a couple more recent ones that stick out:
Back in February, two copies of Mass Effect 2 CE popped up at the Wal-Mart that is literally like 2 miles from my house. I go in there at least twice a week, and ALWAYS scan the video game section. These just showed up out of the blue. Cost? $40/ea.
A bit ago, I was out of town, and found myself being called to a Wal Mart in kind of a rough neighborhood. I had been there about 3 months before, and found some decent old stuff, but something told me to drop back by. Went in, found 6 copies of Tales of the Abyss ($15/ea), 1 copy of .dot hack redemption (was $20, I believe), and 1 copy of DBZ 3 for the Wii ($15). Funnily enough, I had actually found 4 copies of Tales of the Abyss at this same store on a previous visit. To really top it off, I had actually found my first copy of DBZ 3 the week before, at another store in my home town for $15, as well.
It's amazing how you can go for so long without seeing a certain game you might be searching for, or that is rare, and then all of a sudden, you will have a streak where it's like you're tripping over them.
Needless to say, both of those trips made my day (or week as it may be). I'll have to think of some other noteworthy purchases.