the first two may have been posted here already, but if not, here they are:
- Dear [not just urban fantasy] Author by kaigou deals with street life in general.
- A User's Guide to PTSD by rachelmanija
- apiphile offers her experiences with ecstasy (there's additional input from others in edits and commentary)
- strangecreature shares about weed/marijuana
- jumpthesnark chats about meth.
and of course, there's always http://www.erowid.com/