I have started a website which lets users to download ebooks in .pdf, .doc, .rtf. .txt and many other format is it illegal for me to run such a site? FilesCabinet.com
If you are not the author of all the e-books you post, then I would really recommend that you either get permission from the original author, or just not post them. Chances are that if you do not ask for permission they will contact your host with a DMCA or complaint.
Yep, sell whatever you like if you wrote it. If it belongs to someone else then you might find yourself in the courts.