Microsoft Tag is a new system to help give you a way to direct people to a URL using the camera on their mobile phone. You can think of it as TinyURL for optics, or Cue Cat on-the-go minus the hokey cat reader (hey, I know lots of people who loved that thing). It's actually a great system to visually direct people to a URL, free text, a vcard, or a dialer. You can sign up for free at http://tag.microsoft.com, and download the app for your phone at gettag.mobi. Tag is available for a number of phones including Windows Mobile, Symbian, Blackberry, Android, and the iPhone.
Tag can link to multiple types of content from web, SMS, e-mail, calendars, maps, or coupons and can be as small as 5/8". There is a great backend as well so you can see analytics on when and where people are reading your tags.