Wow. I see it around $35 on Amazon, and I know that I didn't pay that much for it around 6 years ago (can't find the order though, so I probably bought it in a large lot of games from Ebay).

A Link to the Past: Bought for $17.56 about 5 years ago, and it seems that I'd be paying around $45-$50 to get it now.

Zelda 2: Adventure of Link: bought for about $5 in 2010, selling for about $15 now.

Oof! This one's the biggest jump I've seen so far. Metal Warriors on SNES. I bought that in 2009 for $40, and the cheapest listing for it on Amazon right now is for $200.