Bitly. I first started using bitly when I wanted to send or post a link to a website, but didn't want to paste long links. It was great. But lately bitly has gotten even better. Now bitly is turning into a social bookmarking site akin to diigo or delicious.
Bitly not only shortens your links, but allows you to create bundles where you can group links into groups based on topics. For example, I can link all my shortened links to my blog posts in a bundle titled, Blog Posts. Handy. You can also share these bundles with others so they can view and/or add to your bundles, making collaborating and group projects even easier.