I've been searching the internet for a truly lossless avi compressor/codec for over five years. Not even HuffYUV is lossless, despite what it says it does.
So, what can you do to perfectly preserve your uncompressed AVI captures?
ARCHIVE WITH WINRAR!
Here's a quick test with different output options:
source: 31 second uncompressed avi file - 630 MB
Now, here's the size of 'encoded' files:
huffyuv codec (default/best settings) - 352 MB [lossy]
rar file (best compression setting + solid archive + recovery record) - 228 MB [lossless]
Uncompressed Full PAL AVI takes up around 1.2 GB/minute. That means that a Blu-ray disc (22.5 GB) would hold, in rar archives, about 50 minutes of video. Not bad!