Off the top of my head, I've got these gems in my instant queue...
MST3K by the dozens...
The Babysitters is pretty hot...
The Gumby Movie
All the X-Files plus both movies
The Fearless Freaks (Flaming Lips semi-doc)
The Spectacular Spider Man (series)
Holy Rollers
A Town Called Panic
Friday the 13th (I-VIII)
Star Trek (I-VI? sans II

)
Though it might not be the most popular genre with this crowd, there are TONS of great anime streaming instantly through NetFlix...
Ninja Scroll
Samurai 7
Blassreiter
Full Metal Alchemist
Voltron
Afro Samurai
Queen's Blade
Golgo 13
Witchblade
etc, etc, etc....
The best resource for Netflix instant watch content that I've found is
Instantwatcher.
They provide the ability to sort the movies so much better than the Netflix home site (by experation date, MPAA Rating, Date of Release, Etc) does and also provide what I consider to be their most compelling feature...a list of what has been added to watch instantly each day.