Jiyuugaoka (自由が丘)
This is originally a residential area but has gradually turned into a popular place for the young people to stroll around. The government has restricted the buildings of this area so that there are no tall buildings here but only 3-4 storeys high buildings. Because of this, this place is especially nice to walk around during sunny days with mild breeze and scents of floweres and trees lining up on the streets. There are numerous cafes (with excellent cakes), bars, restaurants scattered in this suburb. This is also a great place for designed home goods/decorations/furnitures and of course fashion. Jiyuugaoka is also a suburb full of esthetic salons, massage places, beauty salons and hair dressers. Many of the shops here are very famous in Tokyo.
For those who has a sweet tongue, you can go for the Sweets Forest where the most famous cake shops and patisseries have a store here. Trust me, it is worth a visit. The cakes are much much better than many cakes shops in France or Italy or in any Asian country.
Also, if you walk pass a second hand shop in this suburb, I suggest that you go in for a look since these shops not only sell second hand items but also many brand new items but at a very attractive discount. (E.g. 90% off retail price)
Sangenchaya (三軒茶屋)
Sangenchaya is also a residential place but with lots and lots of Izakayas (居酒屋) - meaning drinking places with a wide variety of snacks. This place is crowded with local university students, fresh graduates, and high-school students due to the cheaper Izakayas here.
Other than Izakayas, there are also some very good Italian restaurants in this suburb.
This is a very good place to have a feel of where local Japanese hang out.