My panoramic photos, which I originally created using the Live Picture, Inc. PhotoVista program, are viewable without a plug-in. You only need a Java-enabled browser to view the images. PhotoVista was purchased by MGI in 1999 and the viewer now has zoom functions accessible from an on-screen toolbar. You can also still zoom in and out using the CTRL A and CTRL Z keys.
NOTE: Stopped working with Windows 7 and Explorer 9. Will try to fix with newer panoramic software one of these days.