I use GotryThis. Here's a blog I wrote about it awhile back.
Organize, Track and Cloak Affiliate Links EASY - GoTryTHIS
I don't do much affiliate marketing personally but use it for many of the links here at 5 Star. Not even for the purpose of cloaking, more so for being able to track my outbound clicks.
It does cloak very well, but the feature I like most is being able to see graphs of which links are getting clicked over time or by date range. I also like being able to see how people got to the links they clicked.
You can use PHP or Htaccess to cloak for free, it's just not as quick and easy.
However remember anytime you cloak or re-direct or change links - you need to test them to be sure they are tracking and passing your cookie.