I'm currently using DeLorme Street Atlas but have used Streets & Trips in the past. These two seem to be the leading computer mapping/routing products and I believe they offer similar capabilities. Several years ago I looked at these plus AAA & National Geographic branded offerings and settled on DeLorme. The primary reason, as I recall, was DeLorme's facility (called vias) for forcing a route through a specific location. I believe that S&T is now much improved in this department but haven't personally looked at it for about five years. I've just recently installed SA2006 and am slowly getting familiar with it. I know it's a wonderful thing but there's a lot of new tricks for this old dog to learn. (I haven't uninstalled SA9, yet:-)
I usually have a printed atlas in the car but seldom open it and can't remember the last time I used a modern printed map for planning. Old maps, both printed and online, are a different story. When a trip involves retracing an old route or trip, old maps are key. Of course, finding current equivalents of old roads and then getting a route to use them can be a fairly challenging "computer game". Fortunately for me, it doesn't require Halo 3 level reflexes.
I do use printed history and guide books. Not for every trip but if a trip is at least a little bit in the future I'll spend some time reading anything related that comes to hand. Sometimes books are readily available for a specific road (e.g., Route 66, Lincoln Highway) or area, and there are bunches of "Ten best trips in/from/near..." publications. Some books (e.g, Horatio's Drive, Blue Highways) will just get you in the mood for a road trip and that's a form of preparation, too.
The information highway certainly provides a lot of input. This forum and other e-groups can provide information and are clearly the place to go with specific questions. Sometimes just putting a town's name into a search engine will turn up something like a museum or historic site I didn't know about. If I'm concerned about finding lodging in real-time, I'll look for, and sometimes book, motels online. But, if I only make one online visit for a trip, it will almost be certainly at RoadsideAmerica. What a great website and you can now enter a city and get a map with attractions marked.
Now, actually following a route is another story.