Good icons can really make a world of difference for an application (web or otherwise). Finding good ones can really be tricky... as I posted some free image sites... heres some free icon sites

http://www.gosquared.com/liquidicity/archives/122
http://www.cocoadev.com/index.pl?RoyaltyFreeIcons
http://browse.deviantart.com/customization/icons/dock/?order=9&alltime=yes
http://yellowicon.com/downloads/
http://fasticon.com/freeware/?p=57

These are very cool and modern looking:
http://www.freeiconsdownload.com

This one also has a list:
http://www.smashingmagazine.com/2007/08/25/20-free-and-fresh-icon-sets/