(Very *few*, actually! Unfortunately, it's hard to find good fics featuring these two.)
* Fishing On the Moon by KKChiTown.
No spoilers. No warnings. Just a nice conversation between Duo and Trowa. :-)
* Goodliness is Next to Cleanliness by avaaricious.
This one is post-EW. The boys are working together at the Preventers. Both boys are rather IC. And there's a shower scene! What more could one ask for? ;) (shonen-ai)
The fic is part one of the Appearances Series. You can find the rest at Facades.
* Dreams of Yellowed Boned by keelywolfe.
This one might seem a little on the strange side, but not surprisingly, very fitting for Trowa. One of them is sick. The other plays doctor. yaoi, lemon. YESSS! *g*
* Talk, Talk, Talk by babaca.
Another one that might seem a little strange. But it really isn't! It made perfect sense to me. ;) Portrays a nice bond between Trowa/Duo.
* Heritage by Erin Cayce.
I really like this one. It portrays a darker, meaner side of Duo. Behold, Shinigami. Yaoi, Angst.