Huffyuv is a lossless video codec created by BenRG (the original developer of AviSynth), patterned after JPEG-LS. It supports RGB, UYVY, and YUY2.
Its homepage used to be at http://math.berkeley.edu/~benrg/huffyuv.html but has disappeared. Version 2.1.1 (binaries and source) is downloadable at Donald Graft's mirror.
Latest Huffyuv can be found here: Huffyuv v2.1.1 CCE SP-Patch v0.2.5, released Dec 22, 2003. Get the file huffyuv_ccesp-patch_025.zip.
Another implementation exists within libavcodec (MPlayer, FFDShow, etc), which extends the format to support YV12.