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This is a pretty cool website with a lot of pieces of music for all sorts of instruments. There is plenty here to check out and try to play! 
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IMSLP is a wonderful resource that has all kinds of music that are currently in the public domain. That means music from Bach, Mozart, Beethoven, and other great composers that you can find and study for free!
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8notes.com is another website with a lot of different music for a lot of different instruments. There are some pop and rock tunes on here as well!
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Everyone's favorite site for buying sheet music. This is where Mr. Todd gets the sheet music for the orchestras. 
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Here is Shazamio's website. The link to the youtube is on this site as well. Check it out and have fun with the pop music!