Henley on Thames would also make a nice day trip for visitors to London. You can take a train from Paddington to Twyford and from there the short ride to Henley. The town reminds me very much of Portsmouth, NH in the US only Henley is much more picturesque IMHO. I loved walking around and browsing in the shops in the town centre. There were loads of restaurants that all looked quite inviting. I'm terrible with names but we had a wonderful meal in a small Italian restaurant in the town centre.
Since it was a sunny day we took a long walk along the Thames and also strolled through some residential streets.
The Red Lion Hotel was lovely, I highly recommend it. We even had afternoon tea in what they call their pub, a very small room with high backed wing chairs, lovely small tables and a fireplace with a roaring fire. The food was wonderful and compared to London prices,was quite inexpensive.