I haven't ordered any plants online yet so none of these links are intended to be recommendations for any of their products. They are just sites I've used for information and inspiration.
www.crocus.co.uk - an online gardening centre. As well as all the plants for sale there are different planting ideas for various effects, situations and temperaments!
www.buckingham-nurseries.co.uk - an online gardening centre, specialising in hedging and trees.
www.bridgemere.co.uk - a huge garden centre in Cheshire.
www.davidaustinroses.com - rose specialist.
www.dobies.co.uk - seeds and plants.
www.suttons-seeds.co.uk - seeds and plants.
www.rhs.org.uk - the Royal Horticultural Society
Wildlife information websites
www.rspb.org - RSPB (Royal Society for the Protection of Birds). Amongst other things there is an A-Z of British birds and some information about gardening for wildlife.
www.uksafari.com - a website for anyone interested in the wildlife and countryside of Great Britain. There are loads of photos.
www.bbc.co.uk/nature/wildfacts - I've used this to check a few identifications.
www.english-nature.org.uk - this site has some information about encouraging wildlife in the garden.
www.metcheck.com - weather forecasts. I use it to work out when would be the best time to mow the lawn!