Has anyone ever used software (on computer, phone or tablet), that can take a song, and change the key?

Basically, I would like something like this because every month I play at church, and they give me a playlist with mp3s, or a YouTube link so I can learn the song. I don't know many church songs, so I basically learn them from the mp3s or videos. Problem is that the sheet music given to me is in the key that we will play in, and almost always is different than the videos.

I am having trouble learning a song when the chords I am playing sound so off to what I'm listening to. Im hoping that there is something that can take a song and change the key....

I saw something for the iPad called Capo3. The reviews are mixed... It looks like it's what I want, but thought I would ask around for recommendations.

Thanks in advance.
Reaper can do this using the ReaPITCH plugin (think that's the correct name - I don't have it on my PC at work to double check).
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You can change the pitch of the entire file in Audacity. The sound quality gets glitchy, but for learning the song it is passable.
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Garageband will do this and also Reaper, Logic Pro and many others. As long as you don't go too far out it works ok. I did this for a while but it was a lot of hassle for little reward so I just use a capo now to play along with the tracks and make positional notes on the lead sheets for rehearsal and performance. I have lead sheets for maybe 100 worship songs in 5 different keys.
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Last edited by Cajundaddy at Feb 26, 2015,
Thanks everyone that took the time to reply to my question. I will look at all the options, and it's great that some of them are free.

Thanks again.