Share a keynote in slideshow mode only
Use iWork.com embedding&nbsp;&nbsp;:)

Since January (Keynote 5.0.5), iWork lets you embed your published presentation and play them in Safari (link contains a demo). Follow the instructions there!

Note that not all transitions will be available, so it won't be a “pixel-for-pixel” in all cases, but I guess it's the best alternative we can get, and it will be 100% compatible with Windows (with the limitation that a recent WebKit browser is required).