Associations:

EIA www.eia.org
IEEE standards.ieee.org
IPC www.ipc.org
JEDEC www.jedec.org

Catalogues:

Digi-Key www.digikey.com
Farnell www.farnellcomponents.com
RS www.rswww.com

Other Links:

Electronic Engineer's Master Online www.eem.com
IPC Calculator www.ipc.org
PCBstandards www.pcbstandards.com
UltraCAD Design www.ultracad.com