This is a fun thread. Let me offer up some suggestions:
Type O Negative--Christian Woman: Actually, just about anything by Type O would be quite interesting. No doubt it would work musically, but there is no way I can imaging James doing the deep gothic vocals that Peter Steele was awesome at.
Garth Brooks---Friends in Low Places: I could envision them trying this as an acoustic cover, but outside of that it's hard to imagine DT taking a stab at country music.
LL Cool J--Mama Said Knock You Out: I guess if Anthrax could have a minor hit with a rap cover, perhaps DT could do the same. However, it would more likely be the MTV Unplugged version they would try.
Falco--Rock Me Amadeus: The juxtiposition of DT's progressive sound and the new wave of the mid 80's tickles my funny bone.
Toni Basil--Mickey: I wonder how many beers it would take to get James to try to sing this one.