Are there any better services to upload wide (10K pixels wide) than flickr? I would like to see some kind of 'fit to screen height' and zooming functionalities.
I like pan0.net most of all. It is free, fast, and makes the panoramas look impressive. It uses a Flash-based spherical panorama viewer, which you can even embed into your own site or blog.
Unlike Gigapan, Panoramio and similar sites, pan0.net takes care of perspective transforms, and allows to view the panorama as if you were rotating the head in a first person shooter, it is not just zooming and panning a large flat image. It is much more immersive.
Self-hosted panorama viewer
If you can afford to pay for hosting, you may choose to host images and a Flash-based or Java-based panorama viewer yourself. There are many choices. Some spherical panorama viewers I am aware of are:
Things not to use
Microsoft Photosynth uses Silverlight, and works only on Windows desktops; not very good for web, because cannot be viewed on Linux and many mobile devices. Installation of Silverlight on Mac is not always working as expected (according to forums).
Quicktime VR, it is not supported in the newer versions of Quicktime anymore (see Last nail in the coffin). It is a dead proprietary format.
I would take a look at Gigapan. Not only do they have hardware and software to create very large panoramas, but they also offer a free photo sharing and upload option.
One of my favorite examples of the Gigapan software in use is of: President Barack Obama's Inaugural Address by David Bergman . This image is 1.47 gigapixels for example.
Other options you might want to look at include:
I've created a photo gallery w/ panorama lightbox.
You can try it by clicking on a panorama in this gallery: http://shuw.github.com/photos
To add a similar gallery to your page follow the instructions here: https://github.com/shuw/flickfastr.