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.