What multivariate testing system/software do you recommend?

Thank you for the question...

If your using WordPress I found a cool plugin I'm getting ready to test and do a case study on called Zentester... The best part is you can try it for FREE.

Check it out here (My Obvious Affiliate link): Zentester

If your using Static HTML or PHP pages then my favorite tool is definitely Conversion Prophet...

You can check it out here (My Affiliate Link): Conversion Prophet

I hope that helps out...

Thanks again,

Derek