TrakQR allows you to create, manage, and track your own dynamic QR codes. You are able to link to a website, send a tweet, contact info, create a map and more.
At any point, you can go back and edit them to do something completely different. One day a code on your business card can link to a blog post, the next day it could send a tweet.
You are also able to access code analytics for each one to see how many people scanned a specific code in the last 24 hours, last 7 days and last 12 months.