Guild Wiki- Wiki is a great source of information for general game related questions including quests, missions, items, armor etc
Guild Wars Guru - Alternative general game information source
Ventari's Corner - Includes thread for selling, buying, price check and give aways
Official GW Site - Says it all
Official GW Community - Interesting reads, especially the 'guilds of the week' to check out what other guilds are about.
http://www.xennon.co.uk/eliteskills/ - A good site for finding elite skill locations