You gotta try ichiran ramen! You won't regret it :) they have many outlets and they are opened mostly 24hours. Ichiran is my top favorite ramen, even though I have only tasted it once.
"Menya Kaijin" is recommended.
Their shio ramen taste very light.
Try their rice ball called "Heshiko yaki", too. It's so delicious when the rice ball is put into the ramen bawl after finishing the noodles, and soaked into soup.http://tabelog.com/en/Tokyo/A1304/A130401/13045287/