Things to do in Denver before I’m dead

I’m heading to Denver for the fabulous annual confab of editorial cartoonists, but–alas–I’ve never spent any time there before. Thus, what would be appreciated from connaisseurs of the Mile High City, would be information and recommendations concerning:

Denver’s best CD store
Its best used book store
Its best dive bar
The coolest thing in town that tourists should but never see (example: in NYC, that would be the subway museum)
Anything else you feel like telling me

Please e-mail chet@rall.com, and thanks in advance for your suggestions.