Invest $1,500 in insulation and maintenance and get over twice that in energy savings the first year.
Install a programmable thermostat (such as Honeywell's 5-2 Programmable Thermostat, $40; available at lowes.com).
You can set it to lower the heat automatically just after you've gone to bed and to warm up the house before the alarm clock rings so that you won't have to put on an overcoat when you wake up.
If you lower the thermostat by 7° from the normal daytime temperature, you'll knock 10% off your heating costs. Connecting the unit is a (warm) breeze; you merely unscrew the low-voltage wires and attach them to the new thermostat.
NEXT: Seal those cracks