two quick fun drives:
lakeshore blvd east out of vegas, left on northshore drive, drive along lake mead to the valley of fire. 3-4 hour round trip from the strip
charleston blvd west out of vegas, right on scenic loop drive through red rock canyon. 2-2.5 hour round trip from the strip.
these are parts of vegas 99.5% of the visitors don't see, great scenery.