Where to buy postcards in London, UK

After a short trip to London, England, I wanted to share some spots I found to purchase postcards.

The Cheapest Cards:  Piccadilly Circus had several cheap touristy souvenir shops.  The least expensive postcards I found were 15 for 1£ at a shop just a few blocks away from the circus (roundabout) near the clock at Leicester (pronounced "Lester") Square.

Best Touristy Cards: The Tower of London gift shops had the best touristy cards if you are not looking for cheap view cards.  The Tower is 900 years old and rich in royal history.  The gift shop outside the gate has as good of a selection of cards as the ones inside (there may be slightly different cards inside, but for the most part it is the same).  I was pressed for time here and did not have the opportunity to purchase any cards.

Best Clever / Graphic Tourist Cards:  Paperchase had some delightful postcards that were not viewcards for 0.60£ each.  I found these at the Kings Cross station, but there are several other stores around town.

Non-Tourist Cards:  Ryman is a office supply / stationery chain.  They also sell some non-touristy postcards for 0.80£ each.

Other Options:

The Victoria & Albert Museum had a nice collection of postcards relating to their exhibits for  0.60£ (There is no admission fee to the museum by the way.)

Shakespeare's Globe had a few Shakespeare themed cards - not many, but for a Shakespeare fan probably worth a visit.  You do not have to pay admission to the exhibit / theater to go to the gift shop.  The gift shop is around the corner from the Swan on Emerson Street.

Royal Mail Postoffices do sell postcards, although I never saw any on display.  I finally asked a clerk when I went to purchase stamps, and he brought out a stack of postcard sets.  Also note that if you want collectible stamps, you have to be persistent.  There are usually other stamps available, you don't have to accept the standard stamp with the Queen's profile.

Where have you found interesting postcards in London?