The National Geographic TOPO! software will download the GPS data from my Garmin GPS60 unit very nicely. It's also the only decent map software that works on my Mac. It's also the same software I used to create the basemap for the Reiter Trails Map.pdf file found on VetteDriver's second link (which was then brought into Photoshop for finishing).
The downside to the TOPO! software is that while it sometimes shows 4x4 trails it doesn't show them all or some of the trails have been shut down.
Other than that it all depends on what maps you're looking for.
NWJeepn.com has a great trail list index with many of the trails mapped w/ their GPS equipment. One thing, though, is that I like to get maps of an entire 4x4 area and NWJeepn.com likes to do only one or a few trails per 8 1/2 x 11 paper.
I do my maps on 11x17. Smaller and more manageable than a big fold out map but large enough to fit a decent trail area on and still be legible. Only downside is not many people have 11x17 printers. . . . but Kinkos and Office Depot do.
Figure out which ORV area you want to play in and then figure out the land management agency. For example, Manastash and Liberty are under the Cle Elum Forest Service Ranger Station which has an on-line trail map available here
. It's tiled into 8 1/2 x 11 PDFs. I took these, tiled them in Photoshops, added additional notes and saved as my Manastash Trail Map.pdf file.
Rimrock is under the Naches Forest Service Ranger Station. And places like Tahuya, Walker Valley, and Elbe are run by WA state DNR (which has maps posted online).