The Criterion Cast, 66 Criterion films will no longer be available on Netflix "Watch Instantly" service as of September 22, 2010. The titles are listed at The Criterion Cast.
Movies seem to rotate off and on of "Watch Instantly," so I wouldn't be surprised to see these titles return to Netflix Instant in the future. In the meantime, you can still check out the films on DVD! Or buy them in the current Deep Discount sale.
I have A CANTERBURY TALE, which I've never seen, arriving soon from Deep Discount!