The Common Darter (Sympetrum striolatum) is a very common dragonfly, often the last remaining species at the end of the season.
The only species likely to be confused with a mature male is the Ruddy Darter, but that has waisted not parallel sides to the thorax, and lacks the Common's cream stripes on the legs. The black line on the frons also descends down the side of the eyes in the ruddy, while only crossing the forehead in the common.
Females however can be problematic, as all the female darters look similar. The cream stripe on the legs is only shared with the Vagrant darter, which will eliminate the Black and Ruddy females, while the Vagrant shares with the ruddy, the descending line from the frons.
This is an insect that varies in appearance as it ages. The photos above and below are of females: the top is elderly, the bottom quite young. Males start out looking similar to females, before turning slowly red.