Blogs-Exchange (BE) is the first community of blogs dedicated to the learning and interchange of languages (Spanish and English so far). Give feedback and write on your own blog as a teacher or student, in tandem, in a group or by yourself. More information at About and BE blog.
Blogs Exchange (BE) es la primera comunidad de blogs dedicada al aprendizaje e intercambio de idiomas (inglés y español, de momento). Aquí puedes dar feedback y escribir en tu propio blog como estudiante o profesor, con tándem, en grupo o por tu cuenta. Más información en About y en el blog de BE.
I'd say that Gabriel's
I'd say that Gabriel's suggestions are pretty good. One other thing to mention is that all the museums are free, which is great, especially if you're a bit skint (skint (jerga) = no tienes mucho dinero).
Another good idea is to visit the big shopping areas like Oxford Street (not too expensive) and Knightsbridge (some VERY expensive shops). The art galleries are also pretty interesting, but aren't always free. Also look into the Old Vic Theatre - at lunchtime they put on plays. The one I saw was really good and it's not too expensive because the price of the ticket includes both the play and your lunch.