Thanks for the replies so far, guys. I'm learning a lot. A couple things
you guys mentioned: Yeah my windows are also leaky, even though I do have
storm windows. In some places I can feel air coming in around the window
frames. I've been going around caulking where I can and I put up the
shrink-wrap window insulation. I also bought a package of fiberglass
batting that I've been using to tear pieces off and stuff in places where
air was pouring in (gaps in baseboards, wind tunnel between a crawl space
and the basement, in the attic around the bathroom light fixtures, etc.) I
even have built-in cabinets in the dining room that fill up with cold air!
The whole place seems to leak like a seive but I feel like I'm slowly
getting a handle on a lot of it.

The other thing we're thinking about is the furnace. We have an old oil
furnace pushing air duct heating and the previous owners (who didn't seem to
care much about efficiency) used 1100 gals of oil last year. We're on pace
to use about 2/3 of that just by keeping it cooler, especially at night, and
by the things I mentioned above. The house is a twin and the people in the
other half bought a new furnace and their heating bills went from
$300-400/mo (what we're paying now) to about $85. And their place is just
as uninsulated as ours, and a little bigger due to a rear addition.

We've only been in the place about 3 months so not surprisingly we're broke
right now, so I'll continue to patch up what I can in the meantime. I think
attic insulation (by professionals) and a new furnace are the two priorities
when we can.

Thanks again,
Nate