Visiting soon: best places to find CDs, used books?

Hi. I'm visiting Boulder for work soon, and am wondering if there's still a good place to find CDs? Apparently the store I went to in Boulder 14 years ago is gone. Shame, because I really liked it.

Also: any particularly good used book stores? Especially interested in math & science and music books.

From a quick google, I've seen these questions come up here in the past, but not for a couple of years.

Thanks!