'Worst online retailers' revealed
Which? survey
ChainReactionCycles.com and wiggle.co.uk are the only 2 sites mentioned I've used, and they've been good for me as suggested in the survey. I've never used 7DayShop.com but I've seen them praised here and elsewhere for good prices and service especially on memory cards.
The full article is probably at Which?'s site but usually their articles are incomplete/son't have the scores unless you're a subscriber. A mate told me that our city's main library subscribes, don't know if that's true for all libraries.