I just checked (via google) several Sikh sites; some hadn’t been updated in a while. This site is probably the most comprehensive I’ve visited; it is the 3HO-run Sikh site. I would actually recommend, for a broader view, a visit to Wikipedia ; at the end of the entry on Sikhism is a listing of links, including links to the Guru Granth, and to Gurbani Kirtan sites where you can listen to audiofiles of kirtan.
Please note that I just provided a link to the main Wikipedia site (at least I hope that I did!); you’ll just have to put “sikhism” into their search function.
Hope this helps!