5. 'River Deep, Mountain High' - Ike & Tina Turner, 'Duets'
Amber Riley and Naya Rivera are arguably two of the show's best voices and this cover of the iconic Ike and Tina Turner classic has become a staple for the pair on the countless tours and shows they've done - and it's not hard to see why. Both of their voices work well together, not overpowering the other, and it's a rollicking, fun song that has inspired a generation perhaps not aware of the song to go seek out the original, acting as complimentary rather than competition, something at odds with their character Mercedes and Santana's initial rivalry. Rivera and Riley's voices are simply gorgeous together and while this won't be the last time we'll see them together on the list, this was the first song that made fans of Mercedes and Santana sit up and take notice of the two sassiest and strongest voices in the glee club.