I'm going to see BB King in the Albert hall in June (only mentioned this because I'm about as excited as you can get
) and I'll be taking my 30D and 50mm1.4 with me. I may stay down there for a few days, purely for photography reasons, and take all my kit for variety. I suppose it depends on what you want to take photos of really, and from what angle. A lot of London is quite cramped in the centre, from what I remember so for structures to be in shot I'll be using the Sigma 12-24. For street photography/candids I'll use the 50mm. I may try the 70-200F4 I've just got, but I don't really see this as a walk around lens, plus walking around with the 50mm attached would attract less attention than a big white lens stuck to the front
Actually, this has just made me realise I'll need more memory cards! Damn!