Here is the best and most wellknown & trusted Diablo 2 Trading Forum:
www.d2jsp.org

Here is a great forum for Diablo 2 USWest Trading:
www.cc-comp.com

Here is a well-known Unofficial Diablo 2 Site:
www.Diabloii.net

Here is the official Blizzard Website:
http://www.blizzard.com/

Here is the Diablo 2 LOD Section of the Blizzard Site: http://www.blizzard.com/diablo2exp/

Here is the Arreat Summit items section, where you can find almost every bit of information about Diablo 2 LOD items & gameplay:
http://www.battle.net/diablo2exp/items/

Here is the Battle.net Forums section for USWest Nonladder Trading:
west NL battle.net trade forums

Here is probably the most safe place to download up-to-date hacks & cheats & bots for Diablo 2 LOD (I wouldn't recommend downloading any cheats, bots, or hacks, and I am not responsible if you download any on the site listed below):
http://newd2event.net/

Here is Ebay (where it all started for me):
http://www.ebay.com

Here is a link to my personal CS-Clan Server, which is the BEST CUSTOM MAP SERVER FOR Counter-Strike 1.6 (My CS name is Sm0x0r):
http://www.nsrplayhouse.com