Here are a few internet sites we love:
http://www.highsierratopix.com/ a great site with an active and very helpful forum on the topic
http://www.backpacking.net/bbs.html another good forum site...more national in scope but has some good information
http://yosemitenews.info/forum/index.php very active site with people who know Yosemite inside and out.
http://tahoetowhitney.com/index.html a very thorough site that covers the wonderful trail (and variations) from Lake Tahoe to Mt. Whitney.
http://www.tarol.com/backpacking.html nice site from a regular poster on backpacking who has great experience in the Southern Sierra.
http://www.highcountryflyfisher.com/ this one is full of great information about....yep--fly fishing in the high sierra! What fun!
http://www.undiscovered-yosemite.com/ a wonderful personal approach to Yosemite by someone who was born there--son of a park naturalist.
http://www.rayjardine.com/ the ultimate guru of ultralight backpacking
This website from volunteers from Desolation Wilderness...http://desowv.org/trail-conditions which has good information on current trail conditions.
http://www.avidbackpackers.com/ is the trip logs of a group of younger guys who backpack around Northern California. Fun stuff, and some good trail information.
http://www.wildbackpacker.com has a good links page, as well as information about backpacking in lots of different areas.
Webcams? try these:
And some National Park Sites:
http://www.nps.gov/seki/index.htm Sequoia/Kings Canyon
And don't forget our National Forests:
And here is an NGO (non-governmental agency) that is working to protect the Sierra: