Frustrated with hearing the constant looping of Top 40 songs on the radio? So was David Samuel, 25, the Burlingame, Calif.-based entrepreneur behind TheDJ.com (www.thedj. com). The website plays streaming-audio songs around the clock on more than 70 deejay-free ”channels” of music ranging from Celtic to Mississippi blues to ska (there’s even an El Nino channel featuring songs with ”rain” in the title). The sound quality is slightly better than AM radio, but because Samuel and his staff have more than 75,000 digitized songs in their library, it would take two or three days of listening to hear the same song twice.