I knit with cashmere, I got some great cashmere yarns off eBay. You want to wash cashmere, the more it gets washed, the softer it gets. I just throw my cashmere in the gentle cycle in the washing machine and dry flat.
I love BR cashmere! It's cheap (since it goes on sale with no fail) and great quality. This year they have this crazy $795cdn TEN-PLY one for men! Holy crap!
J. Crew & BR are good for "basic" sweaters. I love Vince and Theory for more unusual cardigans. Some of the Saks Fifth Avenue's in-house cashmere is really nice too.