Just adding my two-penn'th for MagicBox -
http://www.magicbox.uk.com - as value for money, and more importantly service have been excellent in my experience. Very fast delivery too.
Penguin have been good - but don't find their customer service line terribly responsive when I've had problems. Felt a bit gutted when all their website ads said 'Ships today or it's free' - but when you read the small print (which I hadn't) it says 'ships next business day or it's free'. Fed back to them and got no apology, just a pointer to small print and that they'd get around to fixing the errant adverts 'soon'. Would still buy from them though.
Big boxes of bikes are cheap at CostCo if there's one near you and you can get membership (or a friend who's a member) - but they normally only have blue.