YOSEMITE NATIONAL PARK

The internet has lots of Yosemite National Park related resources.
Here is a sampling:

The National Park Service's Yosemite website has lots of general information regarding many aspects of the park.

Aramark is the concessionaire for the park. Their website is a great for finding out the specifics of dining, rafting, tours, biking and other activities that they operate inside the national park.

Yosemite Conservancy is a non profit educational and support organization that also has webcams showing El Capitan, Half Dome, High Sierra and Yosemite Falls 24/7, all year long. The Yosemite Falls cam actually streams a real time video of the falls! The organization provides grants to Yosemite National Park based on the highest-priority needs of the park. Their website is very useful for finding out about art workshops, the Yosemite Theater, lots of Yosemite related books, opportunities to volunteer, donate and more.

For road conditions the Park service has this useful page.

The park service also has this page that posts wintertime road conditions.

Maps:

An important aid in planning your trip. Essential for understanding the topography and location of the different attractions in the park and surrounding areas.

This park service page has downloadable versions of the official maps of the park

Here is another map page from the park service that has several topographic maps of the Yosemite area as well as trail descriptions.

Here is a topographic map of the park from California State University, Sacramento.

This is a very large and detailed topo of the park and may take a moment to download. (local)

This map shows parts of Mariposa County, the town of Oakhurst, and vicinity.