The concept of usubility has really assumed great importance across all the modern day computing systems/applications. Here are a few links on different writeups/articles on this subject:
The hub:
Jakob Nielsen's Website: http://www.useit.com/
Usability Testing Basics:
http://www.cu.edu/irm/stds/usability/
Usability Testing Basics BY Jeffrey Graham
http://www.clickz.com/experts/brand/emkt_strat/article.php/826491
General Concepts of Usability Testing
http://jthom.best.vwh.net/usability/general.htm
Mike Kuniavsky. “Why User Testing Is Good.” Hotwired. April 1998.
http://www.hotwired.com/webmonkey/98/14/index3a.html
Usability Testing in Practice by Andrew Starling:
http://wdvl.internet.com/Authoring/Design/UsabilityTesting/
Usability Testing of web apps:
Usability Testing of World Wide Web Sites
http://stats.bls.gov/ore/htm_papers/st960150.htm
Usability Testing of Advanced Web Concepts
http://www.sun.com/980113/sunonnet/concepts.html
“Jared Spool” and Web Site Usability:
http://www.uie.com
User Interface Design for Sun Microsystem's Internal Web. 1995. By Jakob Neilsen and Darrell Sano:
http://www.sun.com/sun-on-the-net/uidesign/sunweb
Joe Gillespie. Web Page Design
http://www.wpdfd.com/wpdhome.htm
Readings:
Papers and presentations from Microsoft's Usability Engineers:
http://www.microsoft.com/usability/publications.htm
It's Not Just Usability By Joel Spolsky
http://www.joelonsoftware.com/articles/NotJustUsability.html
"TESTING FOR USABILITY IN THE DESIGN OF A NEW INFORMATION GATEWAY" by by Michelle Clairmont, Ruth Dickstein and Vicki Mills:
http://dizzy.library.arizona.edu/library/teams/access9798/lft2paper.htm