Pumpkinseed sunfish

The red 'ear' is a giveaway of pumpkinseeds (as well as redear sunfish, which lack the pumpkinseed's vividly-contrasting stippling and striped face).

I'd agree with LuckyLogan that this looks like a pumpkinseed. They are easily confused with bluegills though and most anglers, even experienced anglers, confuse the two species. Note the red spot on the "ear" and the yellow belly. Bluegills typically have a yellow or orange throat and bluish areas just under the gills and no red spot on the gill. While many sunfish species overlap in color and patterns, thus making ID difficult using color alone, this really does look like a typical pumpkinseed.

Not so sure this is a blue gill, check out Lepomis gibbosus (Pumpkinseed)