Not too far from JP Yoyogi station is a place called Isoji, a well-regarded shop that was on a couple of Tokyo television programs late last year. At 1:30 PM on a Saturday when many people would have been going to do hanami at nearby Yoyogi Park, there was a line of 5-10 people out front. Once you get inside there are 3-4 chairs to sit on. The toku (得 = advantage, gain) tsukemen consists of three thin but decent slices of chashu and a few menmas on top of a bed of tsukemen noodles. The noodles were very mochimochi (springy like rice mochi) and there was a very large portion of them. At the time of order, you will be asked whether you want yuzu flavoring (from a fresh-squeezed one, yuzu is a lemon/lime like citrus fruit) added to your dipping sauce. I opted to do so and it was good. The soup base is tonkotsu gyoukai, like Tetsu or Rokurinsha, but with less taste in my opinion, a thinner mixture. Not a lot of texture either, but a generous amount of onions. The shop is easy to miss as it has no protruding sign, just a blue noren hanging out. It's also right next to a soba place "Yamazaki Tsukesoba" that I will have to investigate on a future trip.
Ramen Livedoor Biz page
Diddlefinger Map (English labels)