any serious website would have HIgh Medium and Low variants of WMP and QT, plus if your keen flash.
Compressor and Media Cleaner Pro will also allow you to export a podcast version and a 3g mobile version. So will Quicktime Pro.
I would for quality and size go with H264 format. it literally blows them all away in filesize and quality.
I only recently exported a clients flash file to a 32 million 10 bit 4:2:2 44khz 16 bit 300 meg uncompressed video file in AVI and MOV for television, as well as supplying them with a podcast and a 3g mobile file.
your website logs will also give you an opportunity to see the most commonly used platform for the videos if you set it up right.