There is a huge discrepancy in baseball card values when it comes to starting pitchers. In my opinion, these three pitchers somehow fly under most collector's radars.
Justin Verlander. Rookie of the year. Has won 17 games in four (soon to be five) of seven seasons. Every season except for two (one being in his first season in which he pitched in two games) he has had a sub 4.00 ERA. Has led the league in strikeouts. Leads all A.L. pitchers with a .839 WHIP this season. All of that, and his rookie cards can be had for less than a buck and you'll find his base cards in the common bins.
David Price. 37-19 career record. 3.43 career ERA. Pitched very well in the post season as a rookie. Second in the Cy Young voting last season and an All Star. Like Verlander, you can find his rookie cards for well below a dollar. I've picked them up for a quarter before.
Dan Haren. Has won at least 14 games five times (soon to be six). Leads the league in strikeout to walk ratio. Three time All Star. A perennial 200 strikeout pitcher. Somehow the guy has played for four different teams over nine seasons, including my beloved Cardinals (that Mulder trade still haunts me). Like the previous two, you can get most of his rookie cards for under a buck and his base and insert cards are normally found in the common bin.