The Pacific Crest Trail is well marked, but other trails and roads in the vicinity, and especially snow cover, can make navigating difficult at times. You must have some kind of maps and descriptions.
If I had more money, I would buy the PCT Atlas by "Eric the Red" (the author's trail name). It has all the information you need condensed into a form that only an experienced long-distance hiker can truly appreciate. It costs $200 and seems perfect in every way.
Next are the official PCT guidebooks from the Pacific Crest Trail Association. You can also buy these on Amazon. These have maps, but perhaps not "perfect" ones, and have lots of information that you might not need. They are also heavy. To make them really usable, you'd need to tear the books apart by sections and mail these to yourself along the way as you need them. They cost around $60 together.
Most people seem to get the official guidebooks along with the data book, which has brief trail notes describing distances between key points on the trail (water sources, roads, etc.). The data book costs $10.
Most past PCT hikers recommend Yogi's guide. This is especially good for planning, it is said, and includes details on what exactly is in trailside towns. It compiles a lot of PCT thru-hiker know-how as well. I might buy this for planning purposes, or borrow one from one of last year's group.
The Pacific Crest Trail CD-ROM costs $30 and includes printable maps; however, I don't find them superior to the ones available for free below.
There is a ton of info and even maps on the web about the Pacific Crest Trail. If all of it were somehow neatly compiled, you'd have an exhaustive PCT guidebook without having to pay anything.
This google-based map of the PCT at Postholer.com allows you to zoom in to exceptional detail. If you had this on a pocket PC or iPhone, you wouldn't need other maps. However, I don't think printing out pages of this map would be easy. And there are better maps than this.
Halfmile's maps are homemade and can be downloaded for free. They have GPS coordinates, water sources, and a very high amount of detail, showing essentially every significant bend of the trail. They also have simple profiles and basic info on trailside towns, including post office hours. I plan to print these out on thin paper and carry sections with me. That's going to be a lot of paper, unless I print the maps back to back or fit two on each side of each page. I'm crossing my fingers that Halfmile finishes the Oregon and Washington sections before the end of April.
Here are some other very nice topo maps just like Halfmile's, but formatted smaller so you can fit more on a page and print out half as many pages of maps. I would go with these if they covered the entire PCT. However, they only go up to section G (less than 25% of the PCT).
At Hikertrash.com you can download maps that are a bit rougher than the previous two sets, but formatted smaller so that you can print out half as many pages of maps as Halfmile's. It also includes a trail profile on top, but one that is perhaps not as useful as Bearcant's (see below). I also find the topo lines hard to read, as they are too close together and all have the same thickness. I might consider these maps, but I appreciate the higher degree of detail on Halfmile's maps. The author has not completed his maps of Central and Northern California or Washington yet, however Oregon is complete.
Bearcant's PCT Elevation Profiler is a superb tool for planning. It shows the trail's ups and downs and the relative location of resupply points and water sources. I plan to print these out and carry them with me. I will transfer key info by hand to these profiles after I print them. These combined with any of the above free maps seem to provide all the topographic information one could ever need.
For me personally, detailed maps are more important than descriptions. I need to be able to orient myself and find important water sources. Research in advance will provide me with what I need to know about trail towns and trail conditions. Therefore, I expect to print out Halfmile's free maps and Bearcant's elevation profiler for on-trail use. I may or may not get Yogi's guide. In addition to the maps, I will make relevant notes in advance about the addresses and hours of post offices and public libraries in towns near the trail, and any other important things that I glean from the web.
This will allow me to get all the info I'll need for under $50, or $20 (paper and printing costs) if I don't buy Yogi's guide.
None of the people making free maps have gotten all the way through Washington yet. I may have to buy the official Washington guidebook to get those maps if they don't finish before I get to southern Oregon.