web automation - Fetch / Send HTTP Post data to a Web Server

Since last two days i am googling for how to fetch and post data on websites using the standard .net aplication.
Such applications will be helpful in many scenarios . Examples of application using the above technique
1) Website Testing
2) Website Downloader
3) Stress testing of Server and Websites
4) Data pulling from websites - like fetching usage data from BSNL Data One server -:)