I use OEC & have been pleased with good software & commisions
I am not sure what you mean by
"free for now, so that I can start trading right away, then open an account later on"
You cant trade with anyone unless you have money in an acct. But if you are still talking about paper trading then they do give 2 weeks or so free mock acct for paper trading so you can try their software. Dont know if the mock acct works on options though. I think it takes 5000 to open acct