Riya isn't the only photo-related site at DEMO. At the moment, Yahoo is demonstrating a new version of Yahoo Photos that looks pretty darn neat--it's all browser-based, but uses plenty of slick drag-and-drop features for a desktop-like feel. This doesn't seem to be live yet and the demonstrator didn't mention when it will be. (I'm going to track down someone who can tell me--I want to use it.)
Vizrea Snap is a service for sharing photos between phones, PCs, and the Web, with built-in blogging tools; the demo (with a 24 theme) is kinding of getting in the way of clearly explaining what the service does.
Smilebox creates sharable digital scrapbooks with fancy graphics and flashy animated effects. (They're Flash-based, so the people you send them to don't need a special application.)
Sharpcast had some technical glitches with their demo of a service called Sharpcast Photos, but it might be worth checking out when it's available this Spring: It's designed to easily sync photo collections between PCs, phones, and the Web (emphasis on the "sync"--part of the idea is that you're always automatically backing up everything).