With the show ending tonight, I thought I would go through and pick out my favorites. There were four that instantly came to mind and I stopped at 12. I will admits, most come from the first three seasons. This will be video heavy so I will cut.
Rumor Has It/Someone Like You - The Troubletones 3x06 "Mash Off"
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Baby It's Cold Outside - Kurt & Blaine - 2x10 "A Very Glee Christmas"
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How Will I Know - Mercedes, Santana, Kurt, Rachel - 3x17 "Dance With Somebody"
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I Want to Hold Your Hand - Kurt - 2x03 "Grilled Cheesus"
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Don't Dream It's Over - Finn & New Directions - 4x09 "Swan Song"
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Teenage Dream - Blaine & the Warblers - 2x06 "Never Been Kissed"
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Single Ladies - Kurt with Tina & Britanny - 1x04 "Preggers"
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River Deep, Mountain High - Santana & Mercedes - 2x04 "Duets"
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Thriller/Heads Will Roll - New Directions - 2x11 "The Sue Sylvester Shuffle"
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Beautiful - Mercedes & New Directions - 1x16 "Home"
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Light Up the World - New Directions - 2x22 "New York"
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Valerie - Santana & New Directions - 2x09 "Special Education"
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Regionals - New Directions - 1x22 "Journey to Regionals"
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And of course where it started---
Don't Stop Believin' - New Directions - 1x01 "Pilot"
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Feel free to add more or discuss what I've posted.