JazzDoubleBass.com is a very nice new site based in the UK. I recently sold them a few articles that they have re-written specifically for bass players. If you play bass it's definitely a site worth checking out.
JazzDoubleBass just posted a great online ear training tool that was developed by Rick, a fellow blogger, who writes a Jazz trumpet blog called I was Doing Alright. Rick's Ear training tool is a beautiful piece of Java script that gives your ear a complete workout; covering intervals, chords, modulations, melodies, key centers, and more.