I prefer not to let Google know too much, therefore I avoid Google analytics Statcounter.com is the way to go (in my opinion)
... and you're a lousy spammer. Hmmm track the returned visitors. What exactly do you mean by this? How and why do you need to track the returned visitors? I will assume you wanted to say "How do you use the free Conversion Tracking tools to help track your ROI" because I don't believe a returned visitor to the same ad (especially if your doing split-testing) is a much value to you. Is it? Well, for this alone you'll need to read some more on Adwords FAQ page. You'll also need access to the thank you page after a visitor buys, because you need to insert a small script code for Adwords to be able to track it. Also, for an affiliate this is a hard task because you need to contact the merchant to include that code for you on their thank you page. PS: The thank you page needs to be newly created just for you even if it is a copy of the original. Because its uniqueness will assure that only your customers visit that page.
If you d't like google analytics then you can try one of these. feedjit.com webstate.com Statcounter.com
Come on, and why do you have to write in bold red characters? Is this the "only" way to get yourself noticed?
Obviously SHOUTING just wasn't enough for this guy! To answer the question though, I'd say Google Analytics, I think as far as free packages go, nothing out there touches Analytics
Well you've done yourself a big favor. We just discovered another idiot on this forum. Enjoy and learn some English. Better answers next time!