Most of these sites are a medium between the freelancer and the person who requires the services of a freelancer. I doubt any site would take on the responsibility of ensuring payment. However, I have heard some sites do provide the facility of an escrow account. You will need to google for information on which sites provide which services.
1)i find some sites for freelance.Anyway their projects need most of technologies. have done only SCJP and SCWCD.Actually i can't fine a project that can do using that two technology.
2)anyway is it ok to write names of the site in this forum?