I've heard this software recommended for Taguichi method testing (although there's some controversy over whether Taguichi is the right thing to use anyway): http://www.splittestaccelerator.com/
HN would be remiss without a mention of A/Bingo, a Ruby on Rails A/B testing framework plugin.
I personally like http://www.phpscenario.org/
It is super simple to set up, runs on my server and is independent of any ad/no-script/whatever blocks.