If you haven't yet given up on cassette tapes, you may be the only one. In 2000, sales of music CDs reached $13.2 billion in the U.S., compared with $626 million in cassette sales, according to the Web site of the Recording Industry Association of America (RIAA). Rock is by far the most popular type of music, garnering a quarter of those sales. But fans of religious music are gaining ground: 7 percent of sales were of this genre in 2001, compared with just 3 percent in 1992. This site also provides reports on listener habits and tastes in PDF format. Most of the good stuff is accessible on the site's â€œMarket Dataâ€? section, such as findings from the RIAA annual survey of music fans, which includes data on demographics and purchasing habits dating back to 1996.