An old-school approach is to get the AAA tourbooks for the area and look up the towns you're passing through or near. Sometimes that's a little more convenient for scanning for interesting things to do than scrolling through items on a GPS screen.
If you're looking for something more specific (e.g. the next Steak 'n' Shake), the GPS wins hands down IMHO. My Magellan has a specific "search along your route" option in addition to the usual "search near here" and "search near this place" options. Probably other makes are similar.