Below you'll find a full list of free state maps available from most state tourism departments. As a fail-safe, I've linked to any state Department of Transportation that also provides free maps, both online and as a phy.
Almost ever states offer a full map in their visitors guide. For the DOT links, virtually all of them offer multiple free, highly detailed online .pdfs of their highways, roads, and other travel methods.
On top of that, many DOTS (I'd guesstimate 40ish) also have some sort of “click here to order a physical map” link. If you're looking for a highway map you can stash in your car's glovebox, this is the link you want to look for on your state's DOT site. You might have to click “highway map” or “road map” before the order form will appear. You might even want to click “Maps” in the menu bar and do a fresh search, because like I said, it's an option for most states!
If you manage to find a dot map or order form that I missed, please let me know. Here's to never getting lost again!
Free Delaware State Map – The only thing I know about Delware is that Vice President Biden lives there and it's the only state without a commercial airport. No wonder people are looking for highway maps here! (de dot map)
Free Florida State Map – When I first made this list in 2009, there was an “Authentic Florida Expert” everywhere on the site. She looked like a stereotypical grandma, but now she's nowhere to be seen. Uh oh, you know what that means… (fl dot map)
Free Idaho State Map – Not only do they have free maps, but Idaho even offers a free children's brochure. It's just a single page that says “hope you like potatoes,” but at least it's something. (id dot map)
Free Indiana State Map – Indiana earns the distinction of being the first state site I've seen with a prominently displayed “free things to do here!” section. I guess that's what it takes to get people to come to anywhere in Indiana outside of Pawnee. (in dot map)
Free Maine State Map – While signing up they want you to “be sure to indicate which regions of Maine and activities interest you.” Uhhh, does eating lobster and telling people I've been to Maine count as interests? (me dot map)
Free Montana State Map – They offer a free winter guide in addition to the state map, but I can give you said guide right here. Step 1: stay inside. Step 2: go outside once spring arrives. (mt dot map)
Free Rhode Island State Map – Their site says “put down that spreadsheet, tear yourself away from your inbox for a second, and fill out this form.” Uhhh … RUN, THEY'RE WATCHING US THROUGH OUR COMPUTERS!! (dot maps)
Free South Dakota State Map – Ok, wait a minute here. South Carolina's slogan: Smiling Faces, Beautiful Places. South Dakota's slogan: Great Faces, Great Places. It's like South Dakota wasn't even trying! (sd dot map)
Free National Park Maps – This website has over 1,600 high-res scans of national parks! You can search by state or alphabetically, as well as download many of them.
That took a lot longer than I thought it would. I need a vacation.