Stay at a green hotel. A green hotel will use shower mounted dispensers, instead of little plastic bottles, and change your linens less often (at your request). Look for a list of green hotels at greenhotels.com.
Go green when you rent a car. Try to rent a hybrid. If this proposition seems scary to you, many rental car companies will happily give you instructions.
Take a vacation with a higher purpose. Check out WildernessVolunteers.org to learn about volunteering on wilderness projects with environmental agencies such as National Park Service.
Buy carbon offsets for your travel. You can donate a little money to websites such as Carbonfund.org and TerraPass.com. This money is used to fund various carbon reducing projects.
Shut down the house before you leave. Even if they are turned off, some appliances continue to use energy. Unplug as much as you can before you head out. Set timers for your lights, if they even need to be on while you are gone.
Check out these cities. Portland, San Francisco, Seattle, Chicago and Oakland are the top "greenest" cities ranked by SustainLane, a green media company.