Hardware:
www.microdirect.co.uk I buy quite a bit of stuff from. Not a huge range, but what they stock is usually priced well.
www.ebuyer.co.uk bigger range than MD, VERY good prices, good postage rates.
I wouldn't bother with dabs, the service is pretty poor these days and prices are only average.
www.overclock.co.uk for all your "special" needs - very good service, expect the delivery within about 10 seconds of pressing the order button! (Well maybe not QUITE that quick)
Software - standard stuff - see above.
Games -
www.gameplay.co.uk - again VERY good service, prices are good and delivery is fast and cheap.
Have fun spending your cash.
