The first and most obvious answer is at home. Countless liquor and convenience stores dot the Japanese landscape offering a myriad of sakes from local breweries and national brands. Take home sake has become more popular in rural areas as the recent crack down on drunk driving has discouraged consumers from visiting sake pubs. Japan's excellent public transportation system is figuratively sake’s best friend since a large percentage of sales are conducted in brewpubs known as izakaya. An izakaya can be many things but most consider them to be small restaurants specializing in fare that is made to compliment sake or other alcohols. Think of an it as a sake pub that serves fantastic food, not greasy bar grub.
The izakayaculture in Japan is at the center of sake perception and consumption. A close second is the after-work-before-train-ride stand up bars and watering holes that also move and promote sake. During the 1980s, many business deals were conducted in karaoke clubs that featured a variety of alcohols. However, the small cups and pouring for others tradition that symbolized sake was at the heart of this very robust drinking period. Things have settled down in terms of the over-the-top consumption, shifting now to the slower paced izakayascene.
Sake in some form is available at most Japanese restaurants but it is hard to find sake in Chinese, Italian, French, and other “western” restaurants. Sake is considered a compliment to seasonal Japanese cuisines but it is not regarded as enough of a compliment to western foods to be available at foreign dining establishments.