The many book stores dotted along this strip can provide hours of inspiration. Aside from those selling new books, several specialise in second-hand and antiquarian books.
Damian Miranda is a graphic designer, photographer and excessive thinker originally from Melbourne, Australia. He currently lives and works as a freelance designer in London.
Maybe an obvious choice, but the Barbican is always good. My favourite space in there is the curve gallery, last time I went was for Cory Arcangel's 'Beat the Champ'. I love the architecture, although not many people do. I think it was voted 'London's ugliest building' in 2003.
The walk along the South Bank from Westminster to Tower Bridge will take you past a plethora or interesting sights and cultural hotspots. There's always something interesting going on too.