Postmodern Jukebox (link)

They do covers of popular songs in a wide variety of styles that somehow consistently work just as well as the originals, if not better. Two of my favorites:

• No Diggity - (link)
• Royals - (link)

Frog Leap Studios (link)

They do metal covers of pop music. Doesn’t appear to have been super active recently, but there’s a nice back catalog of tracks to enjoy. Two of my favorites:

• Africa - (link)
• Uptown Funk - (link)