I usually print out custom topo maps for my needs using National Geographic's TOPO! software. I just used one last weekend while backpacking in Yosemite. I like being able to add my custom waypoints and tracks/routes, setting the print area and coordinate system, printing 2-sided maps, etc. Depending on the weather or other variables, I will print on regular paper or NG's waterproof "Adventure Paper".
I have several full-size USGS quad topos that I've picked up over the years from REI, the USGS in Menlo Park (they have a full map room/store), and other map sellers, but generally they're a pain in the rear to use compared to my custom maps, software-based topos (on laptop, GPS, etc.), and topo map books like DeLorme's.