I love Instant Watch.
When it was first launched there wasn't much content on there, but now there's TONS of great stuff.
I watch Netflix movies more through IW than I do physical disks, now. And the recent change to unlimited viewing is great.
I really wish they didn't use Microsoft's DRM so that you could watch from Macs or from Linux. But overall, it's great.
Just watched on instant watch, recommended to everyone:
The Man from Earth (2007)
The Nazis: A warning from History (fascinating documentary series on the rise of Nazism in post WWI germany, through the fall of Hitler)