Some interesting links:
Urbanspoon London: I like this site because it mixes all kinds of reviews, from critics, food bloggers and anyone who wants to post feedback about a place. I joined them on the first of May 2009. My personal page there can be seen at http://www.urbanspoon.com/u/profile/278364/Trusted-Gourmet.html. I post reviews without photos there. The ones with photos are posted here.
London Eating: it has a very complete database of restaurants and reviews. The reviews can be fake as anyone can post there. It is obvious some positive reviews are posted by restaurant owners and some negative reviews by competitors. Still, it is an interesting site and the offers section can be worth looking at. For example in the past there was an excellent 3 courses lunch set menu for £15 if I remember well at Mini-mundus (now Bellevue Rendez-vous). I used the 50% “deal” when I went to Albannach. Just as well because it was very overpriced and also because that “deal” happens quite often. Tourists going there because of its location at Trafalgar square probably pay the full price…
TopTable: it is like London Eating. Only users who have booked and dined through toptable can write reviews, but that does not prevent fake reviews by restaurant owners booking for themselves. Check its special offers page, it can help your wallet.