For electronica, I'd go for Oxygene and Equinoxe by Jean Michel Jarre. These were absolutely ground-breaking for their time, however Jarre seems to have forgotten why with his more recent concerts. Other people might recommend early Kraftwerk, but I haven't heard them.
My classical experience is a bit limited, by comparison, but I do know a few gems. Holst's The Planets is a worthwhile inclusion. Wagner's Ride of the Valkyries is good, but I'd be fussy about the orchestra (I have one that is only average). For classical crossover, I'd suggest Bond's first album (Born).
Wade.