Opera and orchestral classical music. I
love listening to them in the car; it's just really ... I dunno, breathtaking? For that matter, I love pseudo-/semi-operatic singers like Josh Groban, Celine Dion and Jim Nabors too.
And country. Nanci Griffith and Keith Urban are playlist staples for me; Rascal Flatts is good too.
Celtic was one of the first genres I really got into; I heard Enya's "Only Time" and was immediately hooked. Then I got into Loreena McKennitt and her blend of Celtic with other genres (she uses electric guitar in her songs <3).
And bands like Matchbox Twenty, Daughtry, The Fray, etc. Love The Fray's piano-driven melodies, very cool. And mainstream American pop a la Kelly Clarkson is my guilty pleasure.