what are the sensors i need for a simple line follower with arduino?
People will vary with what they do, but the last one I built I used three photoresistors from radioshack. I believe I bought a pack of 5-6 for 5 bucks.
Fun simple beginner project.
Aren't photo-transistors better to use with some IR led?
Depends on the IR characteristics of the track.
What may appear to the eye to be a distinct line may not be so in IR.