The Quicktime Wiki at Wikicities has a great tutorial for compressing video at low bit rates while retaining a high quality.
Certain codecs and settings can be used to achieve high quality to perceptually lossless compression at relatively low bit rates. This tutorial is intended to demystify the process.
The tutorial requires Quicktime Pro (sorry), but looks like a good starting point. I've done minimal video encoding with Quicktime Pro, but what I have done has been relatively unsuccessful due to lack of a good starting point. This tutorial would definitely have helped.
You do much video encoding? Give us a little insight into your tips and tricks in the comments or at tips at lifehacker.com.
Tutorial:High quality at low bit rates [Wikicities]