Books I recommend for identifying dragonflies and other insects:

-- Insects: Their Natural History and Diversity

-- Dragonfiles and Damselflies of the East

-- Dragonflies of the North Woods

-- Damselflies of Minnesota, Wisconsin & Michigan

-- Dragonflies and Damselflies of Georgia And the Southeast

-- Dragonflies and Damselflies of Texas and the South-Central States

-- Damselflies of the Northeast

-- Damselflies of Alberta: Flying Neon Toothpicks in the Grass