Fuji Soba, found all over downtown Tokyo, is a soba shop like many that have a relatively simple menu of either soba or udon, cold or in hot broth, with the option of a small rice bowl. This place has got to have some of the absolute fastest service I have ever seen, provided it isn't too busy.
After you choose your meal item at the ticket machine, walk to the cook and give him or her your ticket, say soba or udon, and have a seat. Often times, within just seconds your meal will be ready, and how fast you consume from that point is up to you.
Here is another site that recommends fuji soba: