The Olympic rings can be found all over the city...I found them hanging from Tower Bridge (the one you saw David Beckham with the torch, pass under on a speed boat, racing toward the opening ceremony), the Serpentine Bridge in Hyde Park, and at King's Cross - St. Pancras Station.
The two Olympic mascots, Wenlock (with his friendship bracelets!) and Mandeville (representing the Paralympics) can be found all over town. I particularly like the one with the Auburn Tiger painted on the side.
I understand the stuffed versions are not flying off the shelves as Olympic merchandisers had hoped but I did find this book bag that I thought was cute!
One of my favorite sights is this huge ball planted in the concrete in the middle of Sloane Square. It is a giant replica of the Olympic standard shot-put measuring 3m in diameter and thrown down from the Olympic Gods.