I use lossless UT codec .avi files for archived masters.
Lagarith is also lossless, and good for archiving .avi masters.
+1 for both UT and Lagarith Lossless.
I've been using the MXF OP1a with the AVCI-100 codec for a while now. They're not technically lossless, but they are Master quality, and a hell of a lot smaller than UT or Lags.
Avid's free DNxHD is free and widely used - the latter may offer some sort of future proofing.
Unlike UT or Lagarith, it is not lossless, but is regarded as master quality. Like the two Jim suggests it does give much smaller files than Lagarith or UT.
On the downside it is Quicktime based, rather than AVI.
I was just going to ask about DNxHD, why is the quicktime format considered a downside?
When using UT which codec would you typically use?