OK.
I read the other thread.
AAA does have nice big maps.
On the other hand, a Rand McNalley US Atlas for $7 gives you a good overview of the major and most minor highways and the fine tuning can be done using google maps/mapquest/pick your favorite.
I-40 across Arizona and New Mexico is absolutely stunning around sunrise and sunset, ties into I-44 at Oklahoma City, which ties into I-70 at St Louis which will get you to DC. (alternatively, you can also pick up I-64 in St Louis and it connects to I-70 in Maryland but goes through "prettier" country - but sounds like fewer of the folks you'd want to see on the trip)
I-70 crosses the entire US, as does I-80 - just by different routes. Again, depends on who you want to roll near.
Kansas and Nebraska in late September/early October are still quite warm on average, with chance for heavy rain and possible frost. (seriously, I've seen it go from sunny and 25C to snowing and -2C over the course of about 4 hours starting at noon)
hints about US highway numbering system - even numbers run E-W, odd numbers run N-S. Smallest odd number is highway 1 on the California coast, smallest even interstate is near the Mexico border.
most states number their interstate exits by mile marker. (if you're at mile marker 68 going East and the sign says gas at exit 80, you'll have about 12 miles to go)
oh, yeah - the pyramid tents at Cabela's are pretty nice, at reasonable cost, and they set up real fast, but they have a center pole which eats some of the available floor space. (I suspect they're similar to what Kimi linked)
good luck!