Well, I do have quite a few Japanese friends, so it's very possible that sake will be served at some point in time. I'm not limiting my choices at all by adding any particular sort of drink, I have enough room for many more bottles of wine/liquor than I have.
It depends what you are into as Sake selection can be far more confusing than wine selection. There are afterall, over 10,000 varieties of sake. Generally, I think a good junmai-daigingo is the safest, most flavorful and logical selection to keep behind a bar. I also think it would be best to stay away from a Nigori sake, for instance, because whilst it is good, it does have a peculiar taste and generally does not appeal to everyone. Even if I were to recommend a few bottles it can be very difficult to find specific types/brands in your area and when you do most of the labels are only written in Japanese! What I would do (and usually do myself) is go to your local Japanese grocer, and ask their advice on a good bottle of junmai-daigingo. Gekkeikan and Ozeki are two of the biggest Sake producers in Japan and always make a decent, dependable bottle; they are also easier to find in the U.S. than alot of the Sakes from smaller producers. Also, if you do have Japanese friends, as you said, make sure to get a bottle of Shochu! The ladies love Chuhai
And don't forget to buy a few choko to serve the sake in!