Frankly, my universal policy these days is that if the supplier can't get it together sufficiently for me to get the item on first redelivery, I just cancel the order and shop elsewhere. There's no point (for me anyway) in being upset about it - pretty much all the big players are bastards and there's nothing at all you can do about it; repeat custom accounts for so little of their business that customer service isn't much of a priority for them - to be fair, given the existence of people like me, who'll happily switch supplier on a GBP5 price difference, it doesn't make sense for it to be.

World of Computers (woc.co.uk) are pretty good at the customer service thing, but obviously their prices are usually a little higher, and the killer for me is that their stock range is limited enough that they're usually just not selling the kit I want to buy :-(.