Just read a great post on thieves and thieving that is a must read for many a DM and players of thieves by E.G. Palmer here: http://oldguardgamingaccoutrements.blogspot.com/2010/12/many-fold-thieves-of-wyrd-greyhawk.html
It's simply chock full of thiefly details that any omnivorous GM/DM should find of value in designing urban environments and the more dastardly residents therein.
I posted an outline for a wider range of thief skills and (sub)classes of thieves that would go along well with that a while back here: http://aeonsnaugauries.blogspot.com/2010/06/thieving-skills-and-who-gets-them.html
Many good posts on thieves in OSR games can be found on Lord Kilgore's Blog here: http://www.lordkilgore.com/tag/thief
Al of Beyond the Black Gate posted a thief class available here: http://beyondtheblackgate.blogspot.com/2009/10/thief.html
Any other thieving posts of any gentle readers would like to share by comment? Feel free to share them I promise to keep the watch off your backs.