Here are some links to professional organizations and websites:

Professional Organizations
1. UsabilityNet - http://www.usabilitynet.org/home.htm
Very nice site, where there is much useful usability info.

2. Usability News – www.usabilitynews.com
News is updated frequently here. If you are interested in knowing what usability is going on globally, Usability News is where you should go.

3. HFES-Human Factors and Ergonomics Society - http://www.hfes.org
A professional organization for Human Factors based in the UK.

4. ACM SIGCHI - http://www.acm.org/sigchi
The CHI (Computer-Human Interaction) Special Interest Group of ACM.

5. http://usability.gov/
This is the governmental website of The Health and Human Service Department of US, where there is also a lot of good usability stuff.

6. The Ergonomics Society - http://www.ergonomics.org.uk/
The Ergonomics Society in the UK.

7. British HCI Group-http://www.bcs-hci.org.uk/
The HCI group in the UK, which is also the home site of Usability News.

8. STC Usability SIG - http://www.stcsig.org/usability/
Usability special interest group of STC. You can access other groups of STC here.

Personal Websites
1. Nielsen Norman Group (NNG) Website No.1- www.useit.com
Jacob Nielsen's website, where you can find abstracts of many research reports and also you can buy articles and reports.

.2. NNG Website No.2- http://www.jnd.org/
Personal website of Don Norman, his books about the psychology of design are globally famous.

3. NNG Website No.3- www.asktog.com
A wonderful website, many articles there.

4. www.uiweb.com
Scott Berkun's website, which collects all his famous UI articles. You can also find many of his articles in MSDN.

Others
Good resources from Microsoft and IBM：
http://msdn.microsoft.com/library/default.asp
http://www-3.ibm.com/ibm/easy/eou_ext.nsf/Publish/558