Comsoleil is a hidden gem of Tokyo. It is located in Daimon, about 3 minutes walk to Daimon subway station. Daimon is on the Oedo line and it is super convenient. It is quite new (it is opened around 2007 i think) and the price is reasonable. (about 10K - 14K yen for a single room).
However, the room is very small, but it is very clean and the furniture is so new that you will enjoy your stay there. Also, the japanese is very good with the interior design and every inch of the room is used. So you have everything you need for your stay.
It has free internet access, which is great for business travellers.
For breakfast, there is a starbucks on the ground floor. Also, 24 hours convenient store, McDonald, Yoshinoya and CoCo Curry is only 3 - 5 mins away. You won't be hungry 24/7.
All in all, it's dirt cheap, for a spotless room and convenient location. It is also quite close to Tokyo Tower (about 20 mins walk) and you can see the Tower at the hotel entrance.
Note: you can reserve through their website, which I think only available in Japanese. However you can write them an email directly in English for reservation.