With friends in town, a trip to Chatuchak Weekend Market (or Jatujak, or simply 'JJ Market') is usually on the menu.  While a visit to this sprawling covered flea market from hell (apparently the world's biggest) is usually done as a last resort for expats living here (or unless you want some particularly unique things), tourists love it.  Everything from used Van sneakers to antique doorknobs to a menagerie of strange animals are available (although the last few times I was there, I couldn't find that section any more), and it certainly makes for an interesting - and hot - day out, usually resulting in a taxi full of bags on the way home.