There are many good observing resources available online. Here are some of the best free web sites and programs.

IYA 2009
In the year 2009, the world celebrated the International Year of Astronomy as it commemorated the 400th anniversary of Galileo's use of a telescope to study the skies, & Kepler's publication of Astronomia Nova.
National Optical Astronomy Observatory
Whether you are a teacher, student, amateur astronomer, or simply interested in learning more about the Universe, NOAO has several programs and resources here that will help you.
A free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope. It is being used in planetarium projectors. Just set your coordinates & go.
Teaching materials developed for the Galileoscope are available on this website for free. We welcome collaboration & the sharing of additional teaching resources too.
WorldWide Telescope
(WWT) enables your computer to function as a virtual telescope, bringing together imagery from the best ground & space-based telescopes in the world.
Google Sky
An extension of Google Earth that will function as a planetarium program in addition to allowing you to access images & data on astronomical objects. Clicking on any object brings up information on the object & links to images.
You are Galileo
Focuses on students recreating Galileo's historic observations. It includes observing guides & logs for several objects. Students can make observations & send them in to receive observing certificates.
Focuses on the Sun, sunspots, & northern lights. Spaceweather posts information on planetary conjunctions, pictures from amateur & professional astronomers & frequently highlight upcoming conjunctions in the night sky.
Heavens Above
Heavens Above is best known for its predictions of visible satellite passes. This site also has information on comets, the Moon and the planets to help you determine what is visible in the night sky.
400 Years of the Telescope
"A Journey of Science, Technology and Thought"
400 Years of the Telescope for Teachers is the website that accompanies the PBS special that aired in 2009.