There is Dunproofin's (thankful mix) remix of Mercy... and now a couple more have cropped up.
Below is a vid and the sound is MERCY 2008 [Mashup Mix Duffy vs Orbital]... Hmmm not sure what I think about this, but at least there are a couple of nice photos.
There is also another remix about - it is the gareth wyn remix (mp3 download here).
And in case you missed it, here is Dunproofin's thankful mix again (but with a different vid created by Damynine
EDIT: Yet another has cropped up. Below is a remix by JayMeister19.