Here are some suggestions (if you like to walk)
http://www.walks.com/ I can recommend Richard as a guide (see below)
Do not make my mistake and buy on the first tour a Discount Walkabout Card holders (If you plan a few walks)
Richard - the man with the honeyed voice and the distinctive red hat - has three careers. He's an actor, a professionally qualified Blue Badge Guide, and he restores old houses. Urbane, witty, and charming - he's the perfect host. He brings authority, panache, and an insider's savvy to his walks.
http://www.secretlondonwalks.co.uk/