FYI: AVI is not a codec but a file format. By default it uses (\"contains\") uncompressed frames or some simple run-length encoding to store data, I believe.
The Avi format is based on the same idea as Wave files (both being called RIFF-files): a container approach with information in the file header about how Windows\' ACM component should decode the blocks of data in the file.
A good codec, IMO, is the Intel Indeo 5.10 codec, which I believe is included with Windows. It has a quick compression option. Compresses video a lot faster than MPEG.