Me:"Corridors of Time" from Chrono Trigger Composed by Yasunori Mitsuda Arrangement by Zohar Video: http://www.youtube.com/watch?v=uSgst7Pq7w4 (not my video)
For piano, Fur Elise. If you don't know what it is, trust me, you'd recognise it if you heard it.
For 'cello, I'm not sure. I can play the cello part for Eine Kleine Nachtmusik (you'd also recognise this one) in a string ensemble, but does that count because it's with a group?
I can play part of a song called A Trumpeter's Lullaby on the trumpet. That's probably the hardest I can play because most trumpet parts are really easy.
Personally I don't believe any song is "Hard" to play. Some maybe more difficult than others. I believe the most difficult thing in playing music is playing it with the feel or emotion of which the artist intended. Which goes with one of my most favorite quotes: "Blues is easy to play, but hard to feel." But I think the most technical song I can play is "Gravemakers and Gunslingers" by Coheed and Cambria. Here is the link for the song: http://www.youtube.com/watch?v=CsIIyhzmBu8
Well not the hardest song that I play on my guitar, but possibly the most impressive song that I do live is an original called "I Want It Now", Which can be found here.
