Maybe not entirely what you're looking for, but I've found Premise by CopyBlogger pretty useful: http://getpremise.com/ It's a WordPress plugin for a one time fee of $165, but if you do some searching you can find affiliate's offering discounts to get it at $95.

You can ignore all the extra features and focus on landing pages, which is where Premise is really good. (I find the membership and checkout features to be a little iffy.) There are a ton of included graphics, style settings, and different ways to layout the pages, though you won't get the large variety of templates that Unbounce has. Premise also comes with a large library of videos and seminars on copywriting, SEO, conversion optimization, etc. You can also integrate it easily with Visual Website Optimizer, and hopefully soon with Google's new Content Experiments.

Overall I find it a pretty good alternative to Unbounce.