My preferred comprehensive ID resources for North America north of Mexico*
- Butterflies | A Swift Guide to Butterflies of North America by Glassberg
- Tiger beetles | A Field Guide to the Tiger Beetles of the United States and Canada by Pearson, et al.
- Dragonflies | Dragonflies and Damselflies of the East (and the western edition) by Paulson
- Bumblebees | Bumble Bees of North America: An Identification Guide by Williams et al.
- Ant genera | Ants of North America: A Guide to the Genera by Fisher & Cover
- Bees genera | The Bee Genera of North and Central America by Michener et al.
- Frogs & Toads | The Frogs and Toads of North America by Elliott, et al. (includes audio)
- Birds | Sibley Guide to Birds by Sibley
- Trees | Sibley Guide to Trees of N. America by Sibley
Other useful comprehensive ID resources, at varying geographic and taxonomic scales
- Birds of Central America | by Vallely & Dyer
- Spiders | Spiders of the World: A Guide to Every Family by Platnick et al.
- Plants of Yosemite | An Illustrated Flora of Yosemite National Park by Botti & Sydoriak (just amazing…)
- Vascular plants of California | Jepson eFlora
- Mosses of California | Jepson eFlora (mosses)
- California herps | Amphibians and reptiles of California by Stebbins & McGinnis
- Hover flies of the Northeastern US | Field Guide to the Flower Flies of Northeastern North America by Skevington, et. al.
- Bird vocalizations of the US | Peterson Field Guide to Bird Sounds of Eastern N. America by Pieplow (see also: Western edition)
- Marine invertebrates of the West Coast | The Light & Smith Manual (4th ed.) by Carlton (also amazing…)
Useful non-comprehensive ID resources
- Insects of New England & New York by Murray
- Caterpillars of Eastern N. America by Wagner
- Kaufman Field Guide to Insects of North America by Eaton & Kaufman
- Tracks and Sign of Insects and Other Invertebrates by Eiseman & Charney
- Lichens of North America by Brodo et al.
- A Field Guide to California Lichens by Sharnoff
- California Mushrooms: The Comprehensive Identification Guide by Desjardin et al.
- Arthropods of North America: BugGuide.net
- Plants of New England: https://gobotany.nativeplanttrust.org/
- Life on earth: iNaturalist.org
- Plants of California: calflora.org
- ID resources for a variety of taxa: idtools.org
*Note that some of these can be very expensive. There are usually decent alternatives available at lower prices or you can find a pdf (email me if you need help). Also note that by comprehensive, I mean “covers all known species in the area.”