Certainly any map will help with caching, or any other use of the GPS.
I have both the Mapsource City Guide, which is great around town, as it gives every street, along with most every business. The Business information is great when traveling, as you can search for a business by name, closest, etc, and when you find it, it gives you the name, address, phone number etc.
I also have the U.S. TOPO map, which is great when off-road, as it gives you more detailed information about dirt road, trails, streams etc.
They're not cheap at around $100 each, but once you need to find the nearest Chevron station when lost in L.A., you'll wonder how you ever got along without one.