Can anyone suggest a good Orientation tour of London that visits the major sights? I did a search and could not find anything? Thanks in advance.

It's been some time since I did this, but I recall a hop-on, hop-off bus as one option. You can buy tickets the same day. I know there are other tours, and am surprised you didn't find them in a search.

You might consider The Big Bus which is a hop on/hop off bus.

www.bigbus.co.uk

Google took me to three such companies
http://www.londonpride.co.uk/
http://www.bigbus.co.uk/
http://www.theoriginaltour.com/

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On my first trip to London I used Big Bus the first day, hopping on/off, and enjoyed it so much I took a different route the second day. The commentary (live) was excellent. Don't take a recorded (headphones) tour - it will put you to sleep. Try to sit on the top of the bus even if the weather isn't great (get the front seat if you can). The view is so much better.