It turns out that while checking u.s. fares are fairly easy, checking overseas stuff is far more complicated.
u.s. fares can be checked on three sites.
www.air-fares.com (click on the cities menu) gives you a good idea of what's available.
also at travelocity (
www.travelocity.com) hit the flight tab and then the "fare listings" button on the lower right. travelocity also has its "dream maps"
Finally day to day, I like sidestep because it checks more airlines than orbitz, but if you do install sidestep, note that you have to change the "my sidestep" settings or it will automatically run everytime you go to a travel site.
Overseas, I've had some luck by going to the web sites of the airport for the overseas city (most of them have it and they have english versions), checking the schedule of flights from place to place and then going to the airline flight. That's how i was recently able to find a cheap flight from copenhagen to lisbon for a relative. (I started at the lisbon airport web site)