^^ a Wall-E? :P
http://www.tgdaily.com/content/view/42637/135/
this one actually doesn't collect the garbage from the street (it does some kind of sweeping though), but you just sms it and it comes to your door (it has gps maps), you put what kind of garbage you're throwing (it will label it for easier recycling later on) and you put your bag in it...
but the main problem with "urban" robots i guess is vandalism. you can't just keep a robot in the wild and let it work on its own...
a thing that could be done is for example uploading a pic of a person or place to the robot, and then release him in the wild and he would search for it. when he finds it, he sends you the gps location, and if it's a person, he follows them and keeps sending you updates. how cool can a robot stalker be?
it might not be very useful as is, but it lets you put different aspects in 1 project. face recognition, geolocation, mobility, wireless communication, ...
you could then make it evil and give him missions. upload a list of targets, and he searches for them and kills them 1 by 1.
personally, the coolest robot i've seen is the tweenbot:
http://www.tweenbots.com/
so simple, but the idea is quiet nice :D