Principality Building Society offer regular savers every now and then. They always have an interest rate that is at the top of the market... two that I took out at the end of 2011 both offered 5% interest. You do not have to be a resident of Wales to take out the products. The accounts can be opened by post; just call a branch and have them send you the forms.
You can have more than one, as long as each is a different product (i.e. Christmas Regular Saver and Local Hero Regular Saver). The amount you save can be varied every month, within the minimum & maximum allowed.
Before the account matures, they send you a maturity instruction form to return. If you don't return it in time, the money goes into an instant access account. Although they charge a fee for sending the matured funds via BACS, there is no fee to have a cheque issued, and they are very prompt issuing it (my last cheque arrived the day after the account matured).
Staff are always very friendly and helpful on the phone.
I would highly recommend Principality Building Society, especially their regular savers.