DeLorme Street Atlas 2004 is surely one of the two best mapping softwares to plan an on the road. Both CDs in the package can be fully installed on your HD and take about 1.13 GB.
This software is very precise and detailed. For example, I was able to find any single restaurant, motel and gas station where I had been in Moab, a little town in Utah.
If you've to choose your first software, probably DeLorme Street Atlas is your best option.

DeLorme Topo USA 4.0 is a great a software. You can use it either to plan a itinerary and, specially, to plan your outdoor activity. The best part of this software is surely its 3D view. It's great to have an idea of all trail's characteristics, as the elevation gain, lenght, height, profile...
More, you can even trace your own new trail and add it to the already big collection of famous trails included in the software's library.
Naturally this software requires pretty fast computers and lot of space on your HD. In the package you'll find 7 CDs: a installation CD plus 6 other CDs each covering a specifical area of the States. The good news is that you can istall only the CD you're interested in. Each one takes about 600 MB of HD space.

Trails Illustrated is a very complete series of interactive maps by the National Geographic. There are CDs for about each American State and other CDs for specifical topics, as the one shown here about National Parks. This one includes maps for Yosemite, Denali, Hawaii Volcanoes, Yellowstone, Shenandoah, Rocky Mountain, Mount Rainier, Arches, Grand Canyon, Zion, Glacier, Great Smoky, Olympic, Grand Teton e Acadia. This software is very well done and includes many famous trails and gives the chance to draw your own ones. The only lack I found refers to the impossibility of tracing the classic famous trails automatically. If you want information about them (as their profile, lenght...) you must first trace them...with all the following disadvantages (try to trace the Angels Landing Trail with all the many bends and making your mouse passing exactly by the few meters wide trail's last part...). Anyway, a good software and a good alternative to the most precise and expensive DeLorme Topo 4.0.

Trail Finder was something new for me. This software works basically with a web access. When you buy the software, you get a web access to more than 30.000 trails' descriptions taken from about 1.000 of the most famous outdoor books. You can simply imagine to have full access to a huge library right from your computer. Read properly the subscription overview since some features are not included in the software price and are to be paid as extras. This is surely a very original product, I tried a demo version in a store and I was extremely impressed of it.

1,001 Hikes in North America is another good software for who's looking for some hiking experience in the USA. This software comes on 1 CD and icludes basically a library of the most famous hikes. Each one is analize in detail with all the information concernig lenght, elevation gain, difficulty,...with nice maps and photos. More, some expert commentates the hike giving interesting information and tips. Anyway don't expect a software like DeLorme Topo 4.0. 1001 Hikes gives you information JUST on the hikes in its library. The map can't be zoomed, which means that from the State map you can only go directly to the hike map.

StreetFinder & TripMaker, is another software that I heven't tied yet. This is the software's description copied and pasted from the official site.

Rand McNally's award-winning StreetFinder® and TripMaker® software is now available in this special 4-CD set, giving you everything you need to plan trips and get accurate city routes right on your computer. Whether you're headed downtown for a business meeting or vacationing across the country, this collection includes extensive mapping systems and exploration guides to make your journeys quick and hassle-free. Rand McNally has provided accurate, dependable, and user-friendly maps in the United States for more than 130 years, so you can always rely on our easy-to-follow, accurate information. Throw in customizable maps, drawing tools, personalized itineraries, and more, and you've got the most reliable source for planning trips on your home PC. Whether you're a frequent business traveler, family vacationer, or outdoor adventurer, this software has what you need to create and enhance the perfect itineraries for your kind of travel. Choose quick or scenic routes, track with GPS (with compatible GPS receiver), plan end of day stops, search street-level detail for major cities … the possibilities are practically endless.