I'm fortunate to have a entire wing (albeit small) of a university library filled with nothing but maps. That includes just about every USGS topo map ever made. It is a great resource. It also has the USFS/BLM maps which I like better, and many other types of maps.
I use this a lot for hunting. However, I'm not entirely sure that they are essential. They do help with finding access points and, more importantly, areas with very few access points. But they don't actually say "Elk here". Only to the extent that they reasonably depict forest and open parks and other habitat are they really all that useful. Google Earth is better, and more up to date for many of these sorts of features.
The two (maps and Google) used together, are far better than either alone.
There is a website (mytopo.com?) that allows you to put together a custom map of just the areas you are interested in. That saves you from having to carry the whole map library for a small area that always occurs at the junction of multiple maps. Very handy and very quick. I highly recommend them.
