Welcome to Tokyo! I just (finally) got settled about a month ago in Yoyogi-Uehara, which is a bit off the expat beaten path but still plenty expat. I've heard it described as the area for expats who want a bit more Japanese experience.

That having been said, I'd second the other posters who said where you live really should depend on where you work. I like that I can walk to Shibuya where I work in a pinch, such as this morning when there was bad construction on the road. Hiroo and Azabu-Juban are also good places that I considered but ended up finding better housing in Uehara; colleagues at work live in both places and really enjoy it (they have kids, I don't, but I'm not sure that'd adjust the preferences between these neighborhoods).

Since moving here, some other areas that I've found and would consider living in are Naga-Meguro, Shimo-kitazawa, and Sangenjaya. Then again, those are all much busier neighborhoods and are also further out from the Yamanote. I did look in the latter two areas, however, and couldn't find what I considered to be high-quality housing. As it is, I ended up on a major street, which has its upsides and downsides (a bit noisy).

But I'd agree with all the posters above that the area of Roppongi that you're looking at right now is good to visit, but not a great place to live.

hamburgler