I just looked up to see if there were any Halo remixes, and while what I found was pretty cool, I was somewhat disappointed. There were only 4 from the game itself, and 2 that were Marathon Remixes more than Halo ones.
So, I'm thinking it'd be pretty cool if someone came up with some epic Halo music from all 3 games.
My favorite music from the game includes
Halo (Halo 1)
Peril (Halo 2)
In Amber Clad (Halo 2)
The Last Spartan (Halo 2)
Earth City (Halo 2)
A Walk in the Woods (Halo 1)
On A Pale Horse (Halo 1)
I think any of these would make some awesome remixes. Some more hardcore ones (more in the style of the Mjolnir Mix from Halo 2) would be awesome too. Just a thought anyway. Halo has way too awesome of a soundtrack to not get many remixes.