The RHS Plant Finder
Great for finding a particular plant. On-line version of the book but more up-to-date.
Useful site with information and links on garden history, historic parks, and botanic collections open to the public in the UK, USA, Europe, Japan, India, and Australia.
RSPB wildlife garden
How to attract wildlife into your garden including advice on the types of wildlife specific plants attract.
Directory of UK-based garden resources including books, advice, suppliers and links to related sites.