I love these piano covers, I've been obsessively listening to them. You my friend, are awesome! In fact, I'm thinking about making a YouTube account of the sole purpose of liking your videos.
In terms of what I'd like to see, It Ends 2: End Harder and Carmeaty Burana are my top choices, followed by Meat Golem and Devil n' Bass.
I'm also a bit curious, how do you make these? Do you get the sheet music from the originals, and play from that, or can you actually tell what each note is? If you can, that makes you extra awesome.
Finally, about that Super Meat Boy piano...ME WANT!
Seriously, nice job designing that.