One of the benefits of Washington State is that they have no income tax.
You may be responsible for a variety of other taxes, or business license
registrations. You'll find all that information here:
As to your corporate income tax for IRS purposes?
If you were to decide to become an S-Corporation, your corporation
would have no taxes at all. You would need to file Form 2553 to
tell IRS about this decision. And, most likely, you need to do
that by March 15, 2006.
If you file as a regular C-Corporation, you will pay 15% on your
profits, up to the first $50,000 of profits. If your profits are
higher, use this table to look up your tax rate.
It would be very wise, especially in your first year of business, to
engage the services of an Enrolled Agent or CPA to help you make
those decisions and to prepare your first tax return.
Good luck in your new business.