I tend to use programs that are available via my internet browser, They typically don't lag if they are the only window I have open and If i have no videos. ;
Lastfm
Last.fm - Listen to free music with internet radio and the largest music catalogue online
Pandora
Pandora Radio - Listen to Free Internet Radio, Find New Music
Online Radio
Online Radio - Free Internet Radio Stations - AOL Music
Hope one of these works for you.