I frequently need help to identify things I come upon on my walks and am always on the look-out for clear, helpful information, preferably with good clear photographs.
The following list features links to some I particularly like:
Buglife – The Invertebrate Conservation Trust: http://www.buglife.org.uk/
Butterfly Conservation: http://butterfly-conservation.org/
Countryside Council for Wales: http://www.ccw.gov.uk/
This is the official government site, very informative & user-friendly
Nature Spot: http://www.naturespot.org.uk/
Excellent identification of the fauna & flora of Leicestershire & Rutland, but useful countrywide; I use it a lot, especially for insect ID.
Plantlife cymru: http://www.plantlife.org.uk/
Wild flora of Wales & places to see it
UK Butterflies : http://www.ukbutterflies.co.uk/
Everything you could want to know about UK species
Wild About Britain: http://www.wildaboutbritain.co.uk/
Thousands of pages on British wildlife, the environment and the great outdoors.
Wild Flower Finder: http://wildflowerfinder.org.uk/
This UK Wild Flower Finder is searchable by colour, month, habitat, number of petals, flower symmetry and includes 1000′s of clear photographs. Plus structural formulae of hundreds of plant compounds: dyes, herbs, poisons, pharmaceuticals, smells, etc.
Woodand Trust – Visit Woods: http://visitwoods.org.uk/
Forestry Commission site