I'll give you my map strategy, although it is not free. I think maps are second in importance only to your rifle/bow for hunting, and no one expects a free rifle, do they?

Buy the DeLorme's mapbook for CO. It'll cost around $20. In that book you've got the equivalent of the 1:100,000 maps other people have mentioned, but for the entire state. You can sit around evenings dreaming up scouting trips and hunts based off the book. Then, when you have narrowed down the place you want to hunt, get the USGS 7.5 minute maps that cover the specific area you will hunt. You'll probably spend another $20 here.

Take the 7.5 minute maps to the local color copy place and have them print up 11" by 17" copies of your hunting area. (Don't let them fold the maps when they run copies!) Then, have them laminate the copy/copies. Now you've got a durable, weatherproof map for hunting. You'll spend another $5 or so here. Total cost: $45.