Tommy didn't have too many mentionable and notable matches on clay so far even though it would be also not correct to say that he completely sucks on clay.
IMO his most impressive run was by far in Stuttgart 1999 (outdoor on clay, not the indoor tournament!) beating French Open Champion Carlos Moya and another very good claycourt player with Alex Corretja.
The best match was the final against Magnus Norman, which he unfortunately lost after leading 2-0 sets. But it was very thrilling and intense in the first three sets and great to watch. And Norman was a more than capable player on clay, too, and has made one good run at the French Open and other clay tournaments.
The result was Norman def. Haas 6-7(6) 4-6 7-6(7) 6-0 6-3.
Carlos --- C'MON Lleyton!!! --- Kiwi!!! --- Jürgen --- Juan
Best of luck to all Germans : Nicolas Kiefer | Rainer Schüttler | Lars | Florian | Tommy