I like the Hotel Russell in Russell Square. Nothing fancy, just a huge old Hotel on the square, a block from the Underground, a decent selection of Pubs and Restaurants in the area, etc.

We usually book them through www.hotelbook.com, they offer some incredible rates on London hotels if there are promotions going on. We have never had a problem with them.

Of course, if they don't have any promotions going on, or the rooms are all full then the rates will be a different story.