Don't cheap out on a toilet. My wife and I recently replaced our builder's grade model with a better performing one and instantly realized a $10/month decrease in our water bill. The replacement is the same GPF (1.6) but we no longer have to flush two or three times to clear the toilet.
Windows can be a huge energy saver. Upgrading any HVAC without looking at the home for leaks can be a 2 step forwards, 1 step back process.
Roof/Attic insulation can also be a large energy saver. If you go that route make sure you have a contractor who understands attic insulation so you don't cause a problem while trying to fix one.
Front loader washing machines take alot less water and energy to run.
Have your dryer duct clean or if necessary re-routed, a clogged dryer duct will make you run the dryer longer as well as being a possible fire hazard.