The quality of a website must be evident from the Onset. 
Any difficulty whether in response time, accuracy of 
information, or ease of use-will compel the user to click 
to a competitor's site. Such problems translate into lost 
of users, lost sales, and poor company image.

To overcome these types of problems, use the following 
techniques:
1. Functionality Testing
2. Usability Testing
3. Navigation Testing
4. Forms Testing
5. Page Content Testing
6. Configuration and Compatibility Testing
7. Reliability and Availability Testing
8. Performance Testing
9. Load Testing
10. Stress Testing
11. Security Testing

For more information, visit:
http://quality-assurance-software-
testing.blogspot.com/2005/08/web-applications-testing.html

Web sites are essentially client/server applications - with 
web servers and 'browser' clients. Consideration should be 
given to the interactions between htm
l pages, TCP/IP communications, Internet connections, 
firewalls, applications that run in web pages (such as  
javascript, plug-in applications(flash, quick time)), and 
applications that run on the server side (such as asp.net, 
database interfaces etc.).

Other considerations might include: 

What are the expected loads on the server (e.g., number of 
hits per unit time?), and what kind of performance is 
required under such loads (such as web server response 
time, database query response times).  
Who is the target audience? What kind of browsers will they 
be using? What kind of connection speeds will they by using?
 
What kind of performance is expected on the client side 
(e.g., how fast should pages appear, how fast should 
animations etc. load and run)? 

Will down time for server and content maintenance/upgrades 
be allowed? how much? 
What kinds of security (firewalls, encryptions, passwords, 
etc.) will be required and what is it expected to do? How 
can it be tested?
 
What processes will be required to manage updates to the 
web site's content, and what are the requirements for 
maintaining, tracking, and controlling page content, 
graphics, links, etc.? 
Which HTML specification will be adhered to? How strictly? 
What variations will be allowed for targeted browsers? 

How will internal and external links be validated and 
updated? how often? 
Can testing be done on the production system, or will a 
separate test system be required? How are browser caching, 
variations in browser option settings, dial-up connection 
variabilities, and real-world internet 'traffic congestion' 
problems to be accounted for in testing? 
How extensive or customized are the server logging and 
reporting requirements; are they considered an integral 
part of the system and do they require testing? 

links concerning web site security - eg.https pages for 
account info in banking website.
Some usability guidelines to  be consider - eg.how 
userfriendly it is.