With the music industry's transition from platters to downloading proceeding at a frantic pace, shops specializing in used CDs are an endangered species. But SecondSpin.com is still here, and how. The firm's Denver branch is 12,000 square feet and offers a killer selection of more than 70,000 discs and 30,000 used movies. Moreover, the store is outfitted with the listening stations and other accoutrements that are common at places that sell new merchandise, but rare at businesses that peddle previously owned items. For folks who have not joined the MP3 generation and don't want to pay new-disc prices, SecondSpin.com offers a last chance.