I have been exporting Premiere Pro 2.0 HD material using a WMV9 codec and 5000 kbps bit rate to get about a 2GB file, which looks and sounds fine.
To show on Vimeo or Exposure Room, it's a good idea to get at least into the 200-400MB range for file size, and DivX seems to work (although it is necessary to go to 1200 kbps). The result pretty much loses its HD properties, and the audio is not good.
Is there a newer codec out there that will give a 3:1 or 5:1 compression, as does DivX,
but preserve some HD quality?

I haven't done anything with Vimeo for about half a year, but they used to have some guidelines on formats and settings. As I recall, they recommended h.264 at 5kbps. There were some other details that I no longer remember. I'd check the support section on Vimeo to see what they say there. You can also search here as this topic has been covered quite extensively.

I can't speak to settings for Exposure Room as I have not used that.

Thanks Tripp,
Yes, those are good parameters for Vimeo, but that will not compress a large file to a smaller one.