We often recommend Flickr to clients as a robust photo management tool because it's fast, easy to use, and offers nice-looking slideshows that can be easily embedded on webpages.
But no-profits looking for more sophisticated slideshow options might consider checking out a new tool we just found called PhotoSnack. While Flickr focuses on photo sharing and organization, PhotoSnack takes online photo album displays to another level. They have a variety of slick, professional-looking photo albums and slideshows that can be embedded on your site. See some examples here.
Free accounts are limited to 250mb and are branded with the PhotoSnack logo, but a premium account is available with 5GB storage and no branding for just $99.99/year.
If you know a site using this or have tested this out on your own, let us know how it goes!