What zoomable image viewers are there? By these I mean tools that one can embed in a website to let a user zoom in on and pan around a high res image, a canonical example being http://www.zoomify.com/ (see the demo on their home page).

Comments on them are welcome. I'm personally looking for something simple and cheap/free which ideally doesn't require Flash, and will accept the answer that comes closest to these requirements. But others who find this question may have different requirements, so all suggestions will be helpful. I have of course searched; I've found Zoomify, http://www.openzoom.org/ and http://code.google.com/p/galapix/ but none seem to meet my requirements, though I could be wrong and others may have more expert comments on these.