i want to build a site similar to www.omegle.com. can any one suggest me some ideas. I think its built usning twisted , orbiter comet server.
Twisted is a good choice. I used it a few years ago to build a server for a browser-based online game I wrote - it kept track of clients, served them replies to Ajax requests, and used HTML5 Server-Sent DOM Events as well. Worked rather painlessly thanks to Twisted's good HTTP library.
For a Python web framework, I personally favor Django. It's quick to get going with it, and it has a lot of functionality out of the box ("batteries included" as it says on their site I think). Pylons is another popular choice.