The "sightseeing" part will consist of several parts of its own (probably 3 or more), because there are quite a lot of pictures I'd like to fit in here. ;-) They aren't really in any particular order...
Piccadilly Circus
Coventry Street
The direct way from Piccadilly Circus to Leicester Square. When I was there on Sunday it looked like this:
Only 2 days later they had already changed the decoration for the Olympics...
Personally I liked the Union Jacks better. ;-) The "London 2012" banners look a bit... boring, I think. *shrugs*
But you could already see flags and other signs for the Olympic Games all over the city.
Leicester Square
The tkts booth was actually the very first thing I went to on Sunday morning. :D I wanted to buy tickets for "One Man, Two Guvnors" on Wednesday (evening performance) and "The Phantom Of The Opera" on Tuesday. I had no problems with "One Man" and got a good seat at quite a good price. :-) "Phantom" was a different matter. The guy told me that they usually do get tickets, but not before Monday, probably only on Tuesday even... I then went back to tkts on Monday morning again, but as they still told me "Tomorrow maybe..." I ended up buying my ticket directly at the Her Majesty's Theatre as I didn't want to take any risks. ;-)
On Monday I also had a look around the "M&M's World" shop, which is really quite big. ;D It was very interesting seeing all the merchandise and stuff and I loved those big tubes with the m&m's in them. *yummy* But I didn't buy anything in the end...