Well I'd say that every ride could use a single riders line. But these rides in particular need them.
X2 @ SFMM
Raging Bull @ SFGAm
Crush's Coaster @ Disneyland Paris (And almost everything else in that resort for that matter).
Here are some of my favorites in no particular order
Airplane!
Idiocracy
Who Framed Roger Rabbit
Citizen Kane
Hitchhikers Guide to the Galaxy
Rat Race
The Prestige
Donnie Darko
Pink Floyd's The Wall
The White Ribbon
Fear and Loathing in Las Vegas
UHF
Into the Wild
Almost all of the Disney/Pixar Movies
Anything with Charlie Chaplin
Time Bandits
This is just a small portion of my total list.
Have you ever done something totally incredible and amazing and you spend so much time being proud and amazed at what you did that it distracts you from something very important that you end up totally forgetting about and start feeling like a freaking idiot for forgetting about it?
I pretty much agree with Robb's counting method with the exception of backyard coasters. But like everyone else has said, it doesn't really matter how you count them.