There are lots of great websites that provide information or advice about backpacking in the Sierra Nevada.  These are just a few of our favorites.  And if you have a site, or know one that you think we should include, drop us a note, and we'll take a look!
These are our favorites forums for discussions about backpacking:  all you need to know about Yosemite, from people who visit there!  and this is a little broader--if covers the whole Sierra Nevada  and this one is for backpackers all over the USA
And some sites about backpacking and the sierra:  We like this ultralight site...  Ray Jardine is the original guru for ultralight hiking  A great site with directions on how to climb just about every peak in the range...and then some!  a huge list of weblinks for hiking everywhere...although most are about the US--excellent list for California  A nice site that's like a magazine about hiking the Sierra.  Lots of good trip reports on this one  A great trip log on the Pacific Crest Trail.
These are our favorite site for information about the parks:  For Sequoia and Kings Canyon  Don't forget the national forests, home to so many wilderness areas
This is the one site we use all the time: Acme mapper< which allows you to print out topo maps (and other overlays) free of charge, and to the scale you prefer.  How much fun is that? HEre's a link to the Ireland Lake area...and you can wander around from here:
Don't forget the USGS store where you can find, order, and print topo maps of any part of the Sierra Nevada.  Did we mention it's FREE?!?