The different auto-tune makes.

[Coldburn]

Rebecca Black - My Moment. One version with, and one without auto-tune. Hear the difference, and prepare to be shocked, awed and amazed.

Auto-tuned: http://www.youtube.com/watch?v=2OxWD85Ngz4&feature=player_embedded
Regular: http://www.youtube.com/watch?v=RTNquPzvbWY&feature=player_embedded

[Wrexsoul]

Could've been real! But I think it's fake :(

Seriously tho - Auto-tune is so lame the way it's used today. It's a pity, too, because it's a very neat effect if used right, and can be a very useful, -minor- tool if used tastefully on someone who can actually sing to begin with. For a (real) example of the lengths auto-tune can go to transform a recording, check these two out (sorry about the ear torture, but it's the best youtube example I know of!):

Original: http://www.stupidvideos.com/video/song_dance/Shane_Sings_Five_Octaves/#269795

Auto-tuned: http://www.youtube.com/watch?v=VsQISnFx2sg

[O Fortuna]

I really enjoyed watching the progression of his facial expression.