Not baseball, but hockey.
Back in the 2004-05 hockey lockout, I got a case of SP Authentic. First case I'd ever purchased and opened. Got quite a few nice cards that I sold for decent money, along with the Rookie Redemptions they put in since there was no rookie crop to speak of. Pulled the Pittsburgh redemption, and sold it before the 2005 draft. I sold the redemption for $60, now the Crosby goes for a few hundred. Whoops.