Check out “The Carpenters with the Royal Philharmonic”. When I first read about this project I thought “Uh, oh!”. Why mess with a good thing? Boy, was I wrong. Richard Carpenter produced, orchestrated and conducted The Royal Philharmonic in a reworking of their classic recordings using the original vocal and instrumental tracks, now with beautiful, lush orchestral arrangements. Not your typical small(ish) orchestral sound of studio orchestras heard on some Rock recordings, but the real deal.
For something completely different musically, try Frank Zappa with the London Symphony vols. 1&2.