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.”