Stay by Rihanna
Also check out: Original song "Rooftops" + covers of "Give Me Love" w/ Jake Coco, "Feeling Good", "Rolling in the Deep" & "Stereo Hearts".
Trivia: She was featured on The Ellen Show a couple of years back.
"Try" by Pink
Also check out: Original song "Catch Me if You Can" + covers of "Wide Awake", "Stronger" & "Fast Car".
Anthem Lights (the boyband feature)
"Just the Way You Are" by Bruno Mars
Also check out: Original song "Hide Your Love Away" + covers of "As Long As You Love Me", One Direction Medley, "Mirrors" + their 2012 Pop Medley.
Trivia: The band have four members, but you might notice (especially if you're watching the videos out of order) that one original member Kyle Kupecky has been replaced with Joey Stamper.
"Give Me Love" by Ed Sheeran
Also check out: Covers of "Stay" & "Lego House"
"Hotel California" by The Eagles
Also check out: Original song "Alone Tonight" + covers of "Bad Romance", "Fast Car" & "Someone Like You".
"Mirrors" by Justine Timberlake
Also check out: Original song "Tell Me It's Fine" + covers of "Georgia On My Mine" & "Wildfire".
"The Man Who Can't Be Moved" by The Script
Also check out: Covers of "Use Somebody", "As Long As You Love Me" & "So Close"
Trivia: He was a contestant on American Idol (Season 9) and was eliminated in Hollywood week.
"Drops of Jupiter" by Train
Also check out: Original song "Waiting for You" + covers of "Troublemaker", "Hallelujah" & "Lego House".
Honorable mentions: Corey Gray, Edei, Jenny Lane, Kait Weston, Nicole Cross & Tim Halperin
Note: Some of these artists may have been or currently signed to record labels (mostly independents) but have yet to make a big splash and need a little bit more exposure. And of course these are my subjective opinions. I also resisted on putting super popular YT artists on this list such as Boyce Avenue, Christina Grimmie, Tyler Ward, Kurt Hugo Schneider, Cimorelli, Kina Grannis etc.. so don't bash me for excluding any. Just post your faves below!
Sources: Artists' YT Channels linked above