A friend of ours recommended us to eat at Ichiran, as we stay in Roppongi area and there's an Ichiran restaurant nearby. They are inexpensive and have one of the tastiest soup base. First of all, you have to buy the ticket for the ramen from the vending machine by the entrance. You bring the ticket to your seat/booth and make your selection on the provided paper and pass the the ticket to the attendant. They will bring a bowl of ramen per order shortly after.
I find the noodles, sliced pork and the soup to be delicious and would not hesitate to recommend people to try. There are better ones, but this one is better than many anyway.