Hi Nick,
KaizenTrack has been around for a few years and has a solid reputation as a multi-variate testing script.
Another option is my product Easy Multi Tracking. It doesn't have some of the features that more expensive testing solutions offer, but it's still an extremely powerful testing tool. You can learn more about it by going here:
Professional Copywriter Reveals His Proven Conversion Boosting Tool That You Can Use To Skyrocket Your Conversion Rates FAST!
Hope that helps,
Mike