For generics, I've heard good things about tabletstoreuk if you are looking for customer support of some sort. That's the only one that comes to mind. Otherwise I'd try other sites that have good reputation. I'd avoid Ebay.
bit of a sales pitch from me but we sell them via our own website and Amazon. If you are looking for peace of mind then buying anything via Amazon is always a good bet, they offer excellent customer protection and if anything goes wrong they will resolve the problem for you via the seller.
Otherwise I can agree that tabletstoreuk are good guys and will not rip you off, and sort out any warranty issued, which lets face it are not unusual with unbranded tablets.