Twelve-spotted skimmer, male and female. (Much better than the blurry snapshot I got in Pennsylvania earlier in the summer.)
The next four shots are all of meadowhawks. The first is, I believe, an adult white-faced, the second an adult cherry-faced or ruby. The latter two are juveniles, and could represent any of the three species. Note that one has the basal half of the wings tinged with amber, while the other's wings are totally clear. This is not diagnostic, just an example of the variation within each of these similar species. Even experts have a hard time separating immature meadowhawks.
This last I haven't been able to confirm, but I suspect it's a juvenile of yet another meadowhawk species, the yellow-legged.
The fact that dragonflies are so difficult (or at least more difficult than birds, for me) is half the fun.