Huffyuv is a Video for Windows digital video codec (fourcc is 'HFYU').
What makes it interesting is that it compresses YUV video losslessly (using Huffman coding, I presume?) pretty fast - and because it's lossless, it blows away Indeo and MJPEG if you really need to do high-quality video grabs. It's also open source. The author - Ben Rudiak-Gould - intended the codec to replace raw YUV.
The only prolem is that the compression it offers is only around 2:1, while lossy codecs get much higher compression - so don't use it unless you're doing short clips or have a really huge hard disk conviniently at hand...