Bandwidth on intranet sites shouldn't be an issue at all (unless you have VPN users, that is). If you don't and it's still crawling, it's probably something to do with the backend than the front-facing structure.
If you are trying to optimise for remote users, some of the same things apply to try and optimise the whole thing:
- Don't use 30 stylesheets - cat them into one
- Don't use 30 JS files, cat them into one
- Consider compressing both JS and CSS using minifiers or the YUI compressor.
- Consider using sprites (images with multiple versions in - eg button-up and button-down, one above the other)
- Obviously, massive images are a no-no
- Make sure you send expires headers to make sure stylesheets/js/images/etc are all cached for a sensible amount of time.
- Make sure your pages aren't ridiculously large. If you're in a controlled environment and you can guarantee JS availability, you might want to page data with AJAX.