Just wanted to bump up this topic to the present day, as it's still very relevant (
www.toptable.co.uk in particular).
Toptable is great for the value conscious (as there are many special offers to be had, that you can only take advantage of by booking on their website) as well as those who are looking for new ideas for restaurants to try, particularly if you are like DH and I and tend to get stuck in a rut.
I use this website frequently and have noticed that they keep getting new restaurants to join, so the options continue to grow and it's a very easy way to book a table (especially when you are at work in an open plan environment and don't want your colleagues knowing you are making a personal phone call, haha).
Happy dining!