I've been using leadsleap for quite some time. What I like is that you can put tags on your shortened links. This is great for A/B testing. You can have several landing pages that link to a same sales or opt-in page using the the same short url with a different tag. Like that you can identify which landing page is the most successful.

It's the only service that I know that offers this for free. I just make shure to take away the footer ads from leads-leap.