I've used my Snap-On puller many times with good results. It's the type that boneheadeddoctor described. Before that I used a slide hammer. Both require that you over pull and the shrink the metal back as close as you can. It's not for the normal novice.

For small dents the method that uses lights to heat the metal works well in skilled hands.

$40 a dent isn't bad especially if paint work is required.