My personal suggestions are the following:
Amy Webb's "Come, Thou Fount of Every Blessing"
Sally DeFord's "In Humility, Our Savior"
Danielle Isaacson's "Praise to the Lord"
Lindy Kerby's "Amazing Grace"
James Koerts's "Joy to the World/O Come, O Come, Immanuel"
Feel free to email me (through the "Contact" page) what arrangements you like best, and I can post your suggestions on here.
Also, if you find that any links on here are incorrect or no longer work, please email me; I would appreciate knowing for the convenience of anyone who looks at this site.
I would also like to know if you find any free solo piano hymn arrangements that I do not have listed on this website.