I've caught myself often running hot water when it's completely unnecessary. This is especially wasteful because everytime you run hot water to a tap, the hot water pipe in between that tap and the hot water heater fills with hot water, and after you're done that hot water sits dissipating the heat making it cool again (and of course if you're air conditioning it means that the air conditioner is doing double duty to get rid of that heat). That's why you have wait each time you run hot water : The water in the pipes lost all their heat from the last time you ran the hot water. If you run it purely to rinse a cup or the like it's just completely a waste. On the same theme, most of us are pretty clean generally (well, excluding a few in the industry who are notorious for their lack of hygiene) and our clothes generally don't get that dirty : There is no reason to use hot water, or even warm water, for the washing machine. Give cold a try and see if your clothes seem any smellier or dirtier (they won't). More than likely you'll find that you were merely washing at a hot or warm setting out of habit and nothing more. Hot water can help clean heavily soiled clothes but it's been some time since my keyboard got grease on me, so for most of us it's completely wasteful to wash clothes in hot water.
Though you can get a lot of hot air on pages like these for free, the conditioned air (cooled or heated) from your furnace or air conditioner took energy (hence it used resources and emitted pollution) and cost you $. So many houses out there have their temperature set to 21 degrees all year long 24/7 and that is just so incredibly wasteful. Pick yourself up a programmable thermostat. During the winter I have the temperature dropping to 16 degrees and it actually is the perfect temperature for sleeping. When we're not here it drops to 15 degrees C (obviously you should worry if you have anything that is sensitive to 15 degrees, however our long haired cats love it). During the summer time of course it will do the opposite and turn off the air conditioning when we don't need it. Obviously you can achieve the exact same thing manually but more often than not you'll forget (which is the problem with any manual process) and won't derive the energy saving benefits. Get a programmable thermostat! We picked up ours for ~$40 CDN at Canadian Tire and it offers 4 programs per day, with a different set of programs each day if that's what is desired.
Almost all modern PCs have a plethora of energy saving features (usually under the umbrella acronym of ACPI), and all major operating systems can take advantage of it. For instance in Windows 2000 there is a hibernate mode that spools the state of the PC to disk and the next time you boot up it very quickly returns to exactly where you were. All relevant new monitors support a power saving mode (DPMS) that reduces their consumption dramatically. If you don't have power saving turned on on your PC then perhaps it's time for you to take a look: The savings on your electric bill can be considerable as a full PC rig can consume over 200W (and hence emit a huge amount of heat, especially laser printers). If you're using a Microsoft Operating System look under power management in your help or for Power Options in your control panel. Experiment with the settings to find the one that inhibits your use of your computer the least. If the power saving is transparent to you then that's a win/win situation.