There is actually still a gap in our tagging system for these. Up to now the lowest place subcategory for towns and cities is suburb (used also in the center).
If you just want to assign a name to an area, you could do this with name=xy associated for instance to an area tagged "landuse=residential". If there are different landuses and/or several polygons you could make a multipolygon to combine the parts under a common name. This will record the name, but it will not denote the kind of subdivison (like neighbourhood), not even the type of features.
feature.
I suggest to continue discussion about this on the [tagging mailing list][1].
[1]: http://lists.openstreetmap.org/listinfo/tagging