I've put together a list of suggested maintenance items organized by how often each should be performed. I'm sure you already do most of these (cough cough....) but it may help to have a list to help remember everything.
NOTE: I highly recommend hiring qualified professionals to perform most of these tasks. Don't risk your safety or the safety of others by trying to do work that you're not trained to do. All AC, furnace, boiler & water heater maintenance should only be performed by a professional. Maintenance is supposed to be preventative, not a source of new problems! If you want to do something but haven't done it before, you might want to hire someone to show you how.
Clean dryer lint trap
Clean front loading washer door gasket
Clean garbage disposal (grind 10 ice cubes)
Clean range burners
Clean dishwashing tub (see Cleaners page for directions)
Clean front-loading washing machine pump filter
Clean range hood grease filter
Check boiler pressure gauge
Clean sink drain (see Cleaners page for directions)
Change furnace filter
Clean dishwasher filter
Septic tank boost (flush 1 packet of yeast)
Test sump pump
Clean gutters
Clean roof valleys
Clean window wells
Clean heat vents
Clean condensate pump
Replace batteries in smoke/CO detectors
Test smoke/CO detectors
Clean & reseal floor tile grout
House water filter replacement
Clean AC condenser with hose
Trim vegetation away from house and AC unit
Check AC condenser fan
Check insulation on AC condenser line
Clean oven burner(s)
Clean/degrease range hood duct
Clean & reseal wall tile grout
Inspect roof
Prevent roof moss (spray with water, vinegar & salt mixture)
Trim trees away from power lines
Well water quality testing
Clean dryer duct and outside vent
Professional - Boiler/furnace tune-up
Inspect for leaks & rust
Test safety & TPR valves
Test emergency shutoff
Burner/manifold maintenance
Professional - Water heater tune-up
Burner maintenance
Test TPR valve
Flush sediment (draw 3-5 gallons from bottom of tank)
Test GFCI outlets (inside & outside)
Clean & reseal stone countertops
Clean refrigerator/freezer coil(s)
Professional - Replace water heater anode rod
Professional - Septic tank service (pump out & inspection)