Not sure if you are looking for F2P, if not then Ultima Online might be your choice even though it's a pretty old game (I would suggest a... *cough cough* server to be honest). You can pretty much look inside other player's and NPCs backpacks and if your Stealing skill is good enough, you can take items without them noticing (there's also a skill that puts you in Stealth). If you fail they will notice and in the case of NPCs they will call the guards.

http://www.uoguide.com/Stealing