I know there is another good Santander credit card deal on this forum, but now you have a choice.
This new deal is for the Santander 123 credit card which has no balance transfer fee. There is a £24 per year product fee, though if you set up the direct debit from a 123 current account, the fee is waived for the first year.
This means that for 123 current account holders there is a total fee of £24 for the 23 months, which on (say) a £7000 balance transfer works out at about 0.35% total.
Additionally, because it has the same 0% period for purchases, you can still use it for purchases and get 3% cashback on petrol and rail travel, 2% at department stores, and 1% at supermarkets, so it's a decent cashback card too.
Obviously for a smaller balance transfer, the £24 fee has a larger % impact, but as other 24 month credit cards typically charge anything between 1.25% and 3%, then this is a good deal for any balance transfers totalling more than about £2000.
Credit to m1chaels on the stoozing forum for bringing this to my attention there!
The other deal is for 15 months 0% with no transfer or product fees at all, and is a very good deal if you don't want to pay any fees at all and don't need / can't profit from the extra 8 months or the extra cashback for purchases:http://www.hotukdeals.com/deals/santander-credit-card-0-balance-transfers-purchases-for-15-months-no-product-bt-2086914
You can also earn £12.62 cashback through TCB which, if successful, halves the cost of this card!