Radiohead are fond of brass instruments (sounds like the band is dying, though) and the occasional strings. Or if you want even more traditional they bang on pans too, but maybe that's *too* alternative
Otherwise Nirvana's Unplugged in NY comes to mind. Accordion, Cello added to acoustic guitar. Bet you already have that one, doncha.
Earlier Corrs songs have a celtic feel (flutes and violins) try "Toss The Feathers", it's a lively instrumental 'dance' song.
Enjoy TradRock!