Johan Van Summeren at Paris-Roubaix (this year excluded)
Matteo Tosatto (this guy never has trouble getting hired for a sprint train)
Servais Knaven (yeah, he won Roubaix, but his career has really been about shepherding Van Petegem, Museeuw, and other Classics stars at TVM and the Lefevre teams)
Pavel Padrnos (not around anymore, but my favorite diesel from the Postal days--which, admittedly, isn't saying much since I'm no fan boy)
Bernhard Eisel (not only because he's really good, but especially because he's able to sit next to Cavendish all the time without getting too annoyed to do his job)
Now, how about dubious domestiques? Vino for Ullrich in '04? Lance for Contador in '09? Hinault for Lemond in '86? Cunego/Simoni at the Giro '04? Greipel for Cavendish, back when they could still share a team bus? I guess lesser stars don't always make for good helpers...