OptimizePress is one of the best-values available for building sales and landing pages. Their membership plugin is wonderful as well. They regularly publish new templates that look great. Their support, though sometimes a little slow, is reliable and knowledgeable.

Extremely customisable Wordpress plugin that's easy to use.

It's really easy to setup a membership site and the landing pages all work really well together so you can create funnels in less time. There are pre-built templates for landing pages, webinars, thank you pages, funnels and more. Love the ability too add in elements into each page which are really nice looking and they can be based on whether someone is a member or not.