I've been trying out ramen all over town (Isshin, Raijin, Santouka, and Kinton), but the Tonkotsu black ramen at Sansotei stands way out from the rest of the crowd for me.
The noodles are springy, the broth is rich, and the "black fungus" (wood ear mushrooms) are a great addition. It's seriously the best around.
(I've also tried the other varieties, including the spicy Tantan, but they don't reach the same level of perfection as the Tonkotsu black, in my opinion)