Depends what you want to do, and in which part of London. Quiet nights appreciating classical music or hedonistic clubs with loud music? Blockbuster musicals or intimate cigar lounges ? West End / City / Clerkenwell / Islington / Brixton / Chiswick / New Cross etc.
"London" isn't homogenous so if you want to expand on your request, you'll probably get some informative answers .