For whatever reason, sometimes I am only able to find one card of certain players. To be considered a One-Card Wonder, a player must have been active since 1991 (when I started paying attention).
I have this 2008 Topps Update card of David Aardsma which is still my only card of the player with the Red Sox. Boston had Aardsma one year too early. His 2008 showed very little of the player who would emerge into the topflight closer for Seattle in 2009 and 2010. Aardsma was 4-2 with a 5.55 ERA. He did have 49 strikeouts in 48 2/3 innings, but his WHIP was an astronomical 1.726. Who knew he would turn into a good closer? Certainly not Boston who traded him after the season for Fabian Williamson, who never made it to Boston. Kind of a bad trade in hindsight.