**** The National Sweet Pea Society's web-site is probably the most generally useful one, with information about membership, articles for sale, shows, book list, culture, trials, pictures of varieties, and related species. There are some fair pictures, though spoiled by watermarks, of varieties growing on cordons. A great thing about this site is that it's kept fairly well up to date. Go to http://www.sweetpeas.org.uk/
*** Royal Horticultural Society: The RHS has a very extensive web-site, (http://www.rhs.org.uk/index.asp) but access to some of the information about Sweet Peas is dispersed through the site and in Adobe page description format. Most AGM awards for Sweet Pea are now listed (find them under Lathyrus) at http://www.rhs.org.uk/plants/documents/AGM2006JuniperusPhylliopsis.pdf
Graham Rice's superb monograph called The SWEET PEA Book is still available in hard-back and soft-back editions, ISBN 0-7134-8737-2 and 0-88192-595-0 respectively. See http://scentedsweetpeas.com or simply http://grahamrice.com
If you can read Dutch you will probably find the Netherlands’ Lathyrus Society’s site very interesting: if you can’t, It’s still worth a visit for the pictures. There are lots of thumbnail pictures taken at their shows this century: look for the “Tentoonstelling” pages and click on “Fotogalerie”. The more recent thumbnails can be clicked to show large versions of the pictures. Go to www.lathyrus-vereniging.nl