She recorded an album with Robert Plant (Raising Sand) that was very well received critically (I'm not sure if it actually sold well).
It is a bit skimpy and, by now, a bit out of date, but Now That I've Found You: A Collection is probably the best single disc introduction to her music.
The album with Robert Plant sold pretty well, yes. Good album too (I have it). I like Alison Krauss a lot, but I like this type of Americana/country-ish/bluegrass type of music in general. It's a bit in the style of that whole post-hippie Californian soft-rock, country-rock, singer/songwriter scene from the 70's that I like a lot. Jackson Browne, Bonnie Raitt, Joni Mitchell, CSN (also great at tennis btw), Neil Young, Linda Ronstadt - I love that stuff. And todays Americana scene reminds me more of that than of the more yie-haw horseshit on my cowboy boots redneck side of country.