Remind101 (for homework) or if you want to write it on the board so students can get to a webpage quickly. Here are some ways to do it:
- Google's shortener is http://goo.gl/ which not only shortens it, but also allows you to track click on it
- Tinyurl is the original shortener. It will allow you to not only shorten a url, but you can also write customized ones (as long as no one else has done so). This is a good idea if you want your students to go to a page continuously (think homework).
- Bitly is one where you can shorten, customize and, if you create your own account, you can keep a list of your shortened and customized urls. So for example here is the one for my AP Comparative students for homework.