Revo - Sand Dream:
https://www.youtube.com/watch?v=D8hCn4no4O8
Mafumafu - Lycoris:
https://www.youtube.com/watch?v=8KUWLBBX31A
Jake Shimabukuro's cover of While My Guitar Gently Weeps:
https://www.youtube.com/watch?v=qw6YL_l2YxA
I'll avoid straight up video game OSTs (because there are way too many good instrumentals in that genre), but have to mention some of my favorite covers:
FFIV Celtic Moon album - Main Theme:
https://www.youtube.com/watch?v=TX2vIjZgxuY
Chrono Trigger The Brink of Time album - World Revolution:
https://www.youtube.com/watch?v=R82onEjEgC4
Tiger covering Chrono Trigger's Corridors of Time:
https://www.youtube.com/watch?v=9h9TtXrw4rw
"If history is to change, let it change! If the world is to be destroyed, so be it! If my fate is to be destroyed...I must simply laugh!!."- Magus