The theme associated with Roxas, the Other Promise, also gained its own orchestral version. Most of the song is spent building up, but the final climax brings both chills to the spine and a tear to the eye.
There's also "Twinkle Twinkle Holidays", an orchestration of the theme used in Christmas Town. While not epic in the same way as the others listed here, it is still worth mentioning.
What takes the cake, though, is the masterpiece known as "The 13th Anthology". Yoko Shimomura took every single track within the games that had used Another Side's central theme (and The Encounter), and worked them together into one goosebump-inducing song.
Yoko Shimomura's second compilation album, Memória!, has a new arrangement of "Vector to the Heavens", Xion's theme. The 1:30 preview needs to be heard.
The "Concert Paraphrase on Dearly Beloved", which is probably the greatest "Dearly Beloved" piano arrangement that exists. This version's epicness comes from the feeling of climbing stairs as you listen to it. With the simple, standard Dearly Beloved at the beginning of the album, this awesome piece bookends the album with a virtuoso presentation of a fairly simple melody.
Darkness of the Unknown--Piano Improvisation by Kiwii216 (who has done other Kingdom Hearts piano remixes) is a serene yet sharp interpretation of the original that manages to capture the style of Kingdom Hearts despite its differences.