One of my favorite freebie tools is offered by ClixSense. If you are posting your referral link on traffic exchanges, blogs, twitter, etc, you should be using the "My Campaign" tool that allows you to track your promotions.
For example, if you are promoting your link on Twitter, all you would have to do is add a &twit to the end of your referral link. ClixSense would then begin to track how many unique hits your link receives and records this info for you to use under your "Affiliates" link. Click on Affiliates and on the drop down, click My Campaigns to see more.
This tool allows you to see lifetime tracking, or you can breakdown the stats into month, week, day, even hour by hour. It's a great tool to help you track which sites are working best to attract referrals and which sites are bringing in refs that stay active.