Kristen, you'll get more advice on London if you post on the UK community board.
You can get some excellent deals on Priceline and Expedia. Do remember many London ( UK and Europe as well) hotels would only have one double bed and if you are a family of more than 2 you need to make sure the hotel you book into has suitable rooms.
It really helps people to answer these types of questions if you can give as much information as possible. Group size, interests, areas you're looking at, price range, time of year, ages etc. The more information that is in the original request, the easier it is for you to get accurate and relevent answers.
You'll get some great ideas on things to do, tour plans and excursions on the UK board if you ask.