Here are some of the resources I have found most useful for preparing to hike the Pacific Crest Trail.
Pacific Crest Trail Association – permits
Halfway Anywhere’s PCT page – tons of useful info, including surveys of PCT through-hikers
Plan Your Hike – especially their user-friendly list of resupply points
Guthook Guide – up-to-date trail information used extensively by thru-hikers. Cost is $30, as of March 2019.
Halfmile – very popular maps and resupply information
PCT Water report – information about where there are reliable water sources, particularly important in the SoCal desert
USDA’s Natural Resources Conservation Service SNOTEL reports – for tracking snowpack, which can affect water availability and trail conditions in the Sierra
Weatherbase – great for getting a feel for temperatures to expect on the trail. (For grins, check out how cold it gets in Idyllwild, near Mt. San Jacinto in the middle of the SoCal “desert” section.)
MacGyver's Travels 