Sho Kuwamoto has ideas on interaction design for RIAs.

This is a good, if not comprehensive, list to think about.

Many of these seem to come from his experience with desktop app. design, and a lot of them were pretty familiar to me from HCI design courses I took in grad school (which is one reason why I usually did my class projects in Flash rather than in HTML, like so many others did – the range of interface/interaction design possibilities is so much greater in an RIA platform).