Thought I'd share the below info as it is money for nothing if you regularly purchase bikes and parts on-line rather than from your LBS.
I've used Quidco quite a few times for on-line purchases, its simple & free to register and most of the larger bike shops have fast payment so the money to your nominated bank account is pretty quick.
To give you an idea of some offers:
4% cash back on bikes and 3.5% on all other bits and bobs
2% on bikes and frames and 3% cb on all other purchase
2% on all sales
7% on all sport and outdoors (not used this one yet but no reason why it wouldn't work on cycling)
6& on all sales (haven't tried this one yet)
3% on all sales
An alternative to cash back is Nectar points. If you have a nectar card to can register it on line and go through their website and also shop at Wiggle, CRC, Evans, Halfords (apologies to the purist).
From my experience all the links work and there are no restrictions if the item is already on sale.
If you are already planning to buy on-line and you are planning to buy from one of the above mentioned shops then you have nothing to lose as its an extra few quid off here and there.
Anyway, hope you find it interesting if you weren't aware of it and I hope I haven't broken any forum rules by mentioning other companies.