One of the most annoying things I have found with Google Earth is it's inability to tell you what USGS 7.5 minute quadrangle you are currently looking at. The USGS 7.5 minute maps are great to have on hand and can be purchased relatively cheap from the USGS store (http://store.usgs.gov) but you need to know what 7.5 minute quadrangle map you want.
I found really cool Google Earth overlay by an Engineering company which lets you see just that. Download the KML file here: http://www.metzgerwillard.us/quads/quads.kml and then open it in Google Earth.
You simply need to check the Search Results box on the left as well as the 7.5x7.5 option underneath it. Then presto, the names of each 7.5 minute quadrangle map will show up as an overlay on the current terrain.
This KML overlay has some other cool features as well. It allows you to overlay topographic maps onto the current Google Earth view. This makes for a good reference to a handheld map if you are trying to match up terrain in Google Earth onto a topographic map you have in front of you.