Hi Anh,
At Mount Vernon , we have a group called Neighborhood friends which are members who live in the surrounding zip codes. We use Geo Areas to determine who is in the group. As people move in and out of the area they are added or removed when there primary address is updated. Extended Services help us set up the update portion of the program. The zip codes are added as table in SQL .
With Geo Area, you can use that to build a dynamic list.
We also added a Geo Area of all constituent within 100 miles of Mount Vernon. The one drawback is an address can only have one Geo Area.