If you want something for everyday urban use, you cant beat a multitool.
A lot of straight up knives are great, especially outdoors or for other, more shady circumstances.
But in an urban setting where you just want a useful tool to have on you at all times, the multitool is the way to go. Generally Leatherman brand is a safe bet.
http://www.fitsmybudget.com/images/T/premier-multitool.jpg
The best thing about this is that the multitool is not a threatening device, but it has the same utility as a knife.
I would say it has much more utility, the pliers alone are worth more than a knife in my opinion.
I carry one that fits into the tiny pocket in my jeans for easy access, and a much bigger one for hiking/traveling.