Like the "Pandamar" SMB hack on one of my multicarts (significant sprite changes, music changed, title screen changed, color palettes modified, &c.)
Or the unlicensed GBADEV.ORG 2004Mbit Competition cart I bought off eBay - All fully-original stuff, "Nintendo Seal of Approval" nowhere to be found. Even states in the intro screen that it has nothing at all to do with the Nintendo company.
Was looking at a copy of "Pokemon Jade" on eBay the other day, but it went up to at least $26 I think, more than I felt like paying for one single-game cartridge.
For that matter, these multicarts and such seem to be hard to find and getting harder. Game stores that take trade-ins won't touch them, so I can't buy them there. They're amazingly sparse on eBay now, too. And the kiosks selling "Power Joy" stuff at the mall disappeared a while back. Rather annoying.