
Asbestos, lead paint, mold and mildew are all issues that come up depending on the age of the home. Find out how each can effect your health and what can be done about it. For example, lead paint is much worse for kids than adults - if you have a family, maybe you want to look for a newer house without any. But, if you're a retired couple, painting over the lead paint with some sort of sealant might be just fine for you.
The Environmental Protection Agency (EPA) site is a wonderful resource, and they're really happy to answer questions. http://www.epa.gov
Find crime statistics at http://www.cityofseattle.net/police/crime/default.htm. Look up sex offenders' residences at http://www.metrokc.gov/sheriff/services/sex_offender_search/. And don't forget the neighborhood police station. Drop by and chat with an officer; they'll be happy to tell you about what goes on near your potential home.
Take the time to drive by the home at different times - on the weekend, a midweek evening, and even during the morning commute. In the middle of a regular workday, every neighborhood is quiet and peaceful. Stop by a local coffeeshop and pick up a copy of any neighborhood weeklies. This will give you the flavor of the neighborhood.