The nicest stuff is H.264, but it will only play on Quicktime 7. If you want it to look like Apple's stuff, you can use this format.
If you have issues with how big it can be, and what players it has to play with, then you have to start making compromises.
For eg. this trailer [
www.apple.com] is 2:24 long at a resolution of 1280x544 and a file size of 115 MB. It looks and sounds fantastic, but can you host 115 MB? And is it OK if only people using Quicktime 7 can see it? If so, fantastic. Use h.264 and AAC sound.
What are your parameters?