Great resource! We have been providing our NonProfit Theme to organizations for several years, and it's always been among our most popular themes. We give away the theme to non-profits in need through our Helping Hands program as well.

I'd have to respectfully disagree with @David. I think WordPress is a great solution for non-profits. Like with any software, there is a small learning curve involved, but it doesn't require a skilled person to use any more so than it requires a skilled person to use Microsoft Word. Particularly if they are using a well designed and intuitive theme. I think the confusion and difficulty for small nonprofits comes from the other steps involved with creating a website — the domain, hosting and installation. We have taken steps to remove that confusion for users with our Instant Setup service.

I think it's a natural choice for non-profits to use an open source CMS created by an organization that is constantly updated, improved and made more secure by a massive community of volunteers.