Yay! I can finally play 'Come as you are'

[ジュナイパー]

My first song was Twinkle Twinkle Little Star on the Viola. {XD}

If you mean more "advanced" music, then a couple of years later I learned Viva La Vida by Coldplay on the Cello. I think.
When I was younger, I watched a lot of Cellists on YouTube (specifically NathanChanCello and ThePianoGuys), and I wanted to try it. So I tried to play Smooth Criminal by Michael Jackson and Rolling in the Deep by Adele (They didn't really work out that well). Afterwards, I tried to play one of my favorite songs, Viva La Vida. And I'm confident to say that I can play it relatively well. After that, I moved on to a more advanced version played by the YouTube group 2Cellos.

For the Piano, I'm trying to play DJ's Got Us Falling In Love Again, just because I really like the way it sounds on the piano.

 

[DoomDoom]

On Guitar, It was californication by the RHCP. As a first song, it was kinda hard.
On Saxophone, it was Joy to the World.

 

[Lucario]

On guitar, it was "wild thing".
On piano, it was probably something from a "teach yourself piano" book.
On launchpad it was MeGaLoVania.