Thank you very much for the amazing responses; I think I ended up with more choices then before :-) This provides me with some great options.

Hampton Court is nice (maybe a 1/2 day trip though). I very much like Bath and Canterbury as well. I agree with many others that you should just pick one place like Bath, Canterbury, Oxford, etc. I think doing Oxford and Blenheim is a bit much in one day, but you should really go to Blenheim if you are already in Oxford ... really enjoyed it. Bath and Canterbury should be full days IMO since there is a ton to see.

I found Stonehenge disappointing.

Bath, Bath, Bath!

I flew to Edinburgh from London for one day on Easy Jet. Cheap and had plenty of time to see most of the main attractions. I loved Edinburgh and if you go there, eat at the Witchery which is right down the hill from Edinburgh Castle. One of the best meals I've ever had. I've heard that the trains sometimes run late so I was afraid to take them. The next time I went to London, I took Premium Tours and went to Bath, Stonehenge and Salisbury. I loved Bath and wish I would have had more time. My sons wanted to see Stonehenge - personally I could have never seen it and not cared. Salisbury was interesting, but if you've seen alot of cathedrals, it's nothing that different. The first time I went to London, I took the train to Windsor for 1/2 day. I enjoyed it - the castle is in the news alot, and the town is very quaint. It was what I expected of an English town, unlike London. Hampton Court which is also a 1/2 day trip from London is my favorite palace. It just depends on what you're interested in.