Multi-Step Forms in WordPress
Update 2013: I currently have found that http://Wufoo.com is the best and easiest solution for multi-page, multi-step forms. They have great tools that allow you to display certain fields depending on the answer to a previous field and to display certain pages or success messages depending on the users previous answers.
I normally use http://contactform7.com – but it doesn’t seem to have the option for multi-step forms. So I’ve found two other solutions (haven’t tried either yet, but I’ll post an update when I do):