1) Has keys (well, more than just a few)
2) Isn't too heavy metal (I like some Metal, though)
3) Not "gag songs" (Parry Gripp and JoCo excluded)
It's hard for me to make a list of 5 songs because I've bought about 70% of the PS3 RBN catalog and continue to make purchases each week.
That said, I'd pick:
1) Jaron and the Long Road to Love- Pray for You
2) Halcyon Way- Inside Looking Out
3) something by Askari Nari (anything)