The Frugal Traveler of the NY Times recently wrote a piece about ramen in Tokyo. The article and accompanying slideshow are mouthwatering. He also put together a Google map of some ramen shops in the city.
View Tokyo's Ramen Shops in a larger map
I have been on a bit of a ramen kick since coming back from Vietnam. One thing I've learned is that the ramen egg is really important to me. It has to be a slow cooked egg so that the yolk is creamy and yummy. I had a hardboiled egg in a bowl this week and it just really ruined things for me. David Chang has a great little write up in his Momofuku cookbook about slow cooked eggs in Japan. You should buy his book if not for the recipes, for the interesting stories.