Has anyone taken one of those Harry Potter tours in London and/or surrounding areas? If you had a good experience with a company, can you pass along the tour company name?
We did well with London Walks. http://www.walks.com/Homepage/Harry_Potter_Tours/default.aspx.
Cost is 6 GBR/person for the normal walk and more for the special day trips.
You can visit Platform 9 3/4 at King's cross station without booking a tour. Just go to King's Cross station and look for it. I won't say anything else so as not to spoil it for you, but it doesn't cost anything. My children loved it!