My clients are primarily Americans. I want to open an LLC in US to let my clients pay me painlessly. I don't plan to have nor office neither employees in US.
Which state should I prefer to incorporate?
And what bank can you advise to work with?
Delaware is widely regarded as having the most LLC friendly environment. One of the start up LLC's with which I am working just incorporated in Delaware. Here's a link to the Delaware Division of Corporations which should be helpful: link text For a bank, I'd suggest leveraging your existing banking relationship and asking your current bank for a recommendation of a US bank with whom they work who would recognize the value of your relationship with your local bank.
I have helped more than a dozen foreign clients form corporations or LLCs in the U.S.
First, some terminology: One forms (rather than incorporates) an LLC; incorporation applies only to corporations.
Your situation is a bit unusual: My clients typically will be operating a business here (not just collecting payments), so they form the LLC or corporation where it makes sense for the business to operate.
In you case, you will need to have your business operate somewhere. You should consider retaining a tax advisor to help you determine whether there might be a financial advantage to forming your LLC in a low-tax state, given the nature and amount of the payments that you will be receiving. You may find "Why (not) form an LLC in Nevada? " helpful.
Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.
I have recently learned about Vermont Virtual Companies, which seem to match your situation perfectly. It's a very new thing though.