Some pretty good recommendations here. I had to think about this one a little bit. I suppose you are referring to full orchestras rather than a few strings. "Pirates" from ELP's Works vol. 1 is great and "Gates of Delerium" from Symphonic Yes uses an orchestra well. However, IMO Alejandro Escovedo's "The Boxing Mirror" uses cellos and violins in a really interesting way to rock. Check out "Deer Head on the Wall" from that album. Escovedo uses a string quartet to complement his electric guitar and the results are very exciting live. "Roomful of Songs" is just a string quartet with no electric guitar, but is a beautiful album. As implied in the posts above, you don't want to devolve into musak elevator music. Strings can be inspirational when applied in creative ways.
Rock with strings
Good day fellow musicheads! This goes against my inner rock child, but as I age (gasp), I find myself digging rock/pop string section Lps. Moody Blues made the definitive expression with Future days and the Zombies Odyssey is amazing. This seems a predominantly British genre, and at times very pretentious (haha), but one has to applaud the ambition. Any other suggestion? Also, I'm pretty content with the sacd version of Future Days, but curious to see what others have. Safe and happy upcoming Turkey Day to all. And...go Lions!