I thought about mentioning tennis, but it's hard to knock a product that spews the occasional gem:
2005 ACE dual jersey auto Federer Sharapova BGS 9.5/10! - eBay (item 140215968614 end time Mar-25-08 14:59:34 PDT)
Federer cards are major hits. His best rookie card /25 has been offered for $3,000+ "regularly" on eBay. Let me know when a bowling card goes for that and I'm ALL about it!!
I love that the non-major sports like hockey (LOL, just kidding) get some cards produced though. I really thought about cracking some cases of tennis to pull a Federer rookie until I did some research and discovered that the only way to get that 3k card is to buy an international set that was pretty hard to come by.
Disc golfing cards ought to be a hit... that needs to be the next sport to bust through!

I've got some friends in the Sacramento area that would be featured as future legends in the sport, LOL!!