Android - What's the easiest way to create a QR code for a link?

Using the goo.gl URL shortener: http://goo.gl/a4Wv and adding a .qr to the end of it: http://goo.gl/a4Wv.qr

The Google Charts API is definitely the easiest. You just make a URL as follows:

https://chart.apis.google.com/chart?chs=150x150&cht=qr&chl=<content>&choe=UTF-8

Content is usually a link, for example, this is a link to this site:

https://chart.apis.google.com/chart?chs=150x150&cht=qr&chl=https://android.stackexchange.com/&choe=UTF-8

You can also make ASCII QR codes (mainly for websites like Reddit): http://asciiqr.com/