We ended up writing our own. We wrote an Image Manipulator that allows people to upload image and then apply effects, such as Drop-Shadow, resize, sepia, crop, etc. They can then add captions and keywords and create different galleries. We have an early version here: http://www.imagetrakker.com
but we've made a lot of improvements to it lately and haven't updated that site yet. We then wrote a user control that our clients can drop onto their site and display a single album or a whole gallery. Again, an early version is here: http://www.waldorfgarden.org/events/index.aspx
though newer versions have more features. The clients can select thumb sizes, whether to show navigation, start in the Gallery view, auto play, etc, depending on their preferences for that particular slideshow.
We're really happy with it, and may make it available to the community at some point. Our clients love it