IPscene - a directory of community groups etc. in the IP postcode - this link is to the Gardening section, but there is so much more on there.
National Gardens Scheme - to find gardens to visit
Suffolk Gardens Trust - who conserve and protect Suffolk Gardens
Garden Organic - for organic gardening and the Heritage Seed Library
Blacksmiths Cottage Nursery - owned by the marvellous Ben Potterton!