These are some links to useful web sites that I use:
the Garden Network
This site is a forum site where many different garden topics are discussed.
RHS Help & Advice
The Royal Horticultural Society have a lot of useful advice on their web site.
A real fount of knowledge, especially on potatoes. The site supplies many different seeds and I have always received a high level of service from them.
A lovely nursery with well-informed helpful staff. They also stock some more obscure plants.
Klondyke Garden Centres
A General Garden Centre with convenient access.