Have a look at Headforpoints (which is travel-oriented and doesn't mention plain-cashback cards) and Moneysavingexpert (which is, bluntly, poverty-oriented).

If you are spending a lot and you fly, there is no better UK spending card IMV than the Barclays Avios Plus; 1.5 avios per pound is worth just over a penny *if cashed in as Nectar to Sainsburys/eBay*, and potentially a lot more if redeemed well on flights.. This is very hard to beat given the low cap on interchange fees. The BA Premium Plus Amex earns Avios at the same rate - and also the highly valuable voucher once a year - but Amex acceptance in the UK is not great.

There's also the new Lloyds Mastercard product, which pays 1% back *in cash* but only 0.5% on the first £15k pa.

Both Barclays and BA Amex have sign-up bonuses which vary from OK to amazing - watch Headforpoints to see when the "good" offers come around.

All these cards have annual/monthly fees so don't work if you don't spend a lot - and hence outside the remit of Moneysavingexpert.