I particularly like old books of Physics. My favorite hunting place for these is Abids and Koti in Hyderabad. There are good number of footpath sellers on Sunday in Hyderabad. I could get IRODOV book almost new for Rs 20/- ( Twenty only).Some of the old book stores in Hyderabad u can get jewels if u have patience. I traced some of the MTG books on Physics Olympiad problems which is a good collection.