NB These links are mostly UK focused.
Bees and Bumblebees:
http://bumblebeeconservation.org/
http://www.nhm.ac.uk/nature-online/life/insects-spiders/identification-guides-and-keys/bumblebees/
http://www.bumblebee.org/quickGuide.htm
http://www.bloomsforbees.co.uk/id-guide/
https://www.buzzaboutbees.net/index.html
Butterflies and Moths:
http://butterfly-conservation.org/
http://www.ukbutterflies.co.uk/identification.php
http://www.britishbutterflies.co.uk/identification.asp
http://www.wildlifeinsight.com/british-caterpillars/
Birds:
http://www.rspb.org.uk/discoverandenjoynature/discoverandlearn/birdidentifier/
http://www.bto.org/about-birds/bird-id
https://www.britishbirdlovers.co.uk/bird-identification
http://www.garden-birds.co.uk/birdgallery.htm
https://www.allaboutbirds.org/guide/ – Cornell University
Bugs/Insects:
http://www.dragonfly-images.co.uk
https://british-dragonflies.org.uk/
http://www.insectidentification.org/
http://www.amentsoc.org/insects/what-bug-is-this/
http://www.ladybird-survey.org/
http://bugguide.net/node/view/15740
Everything (or at least a wide range of wildlife):
http://www.ispotnature.org/communities/uk-and-ireland
https://www.wildlifetrusts.org/
http://www.britishnatureguide.com/
http://www.wildlifeinsight.com/