If you live in California there's an annual minimum franchise tax of $800, plus whatever annual fees are charged by the state you incorporate your LLC in.
My unused CA S-Corp has been the bane of my existence lately. From the $800 fee to the documentation required to stay in good standing (small, but easy to forget when the company does nothing), it's more pain than it's worth.
If you're someone with lots of ideas and lots of peaks of excitement, it actually might better to postpone incorporation until you can't responsibly continue without some sort of limited liability.
Which is why we invented http://foundrs.com, which is a way to have your cake and eat it too. Don't pay any taxes until your business takes off (at which point you should incorporate), but have a good founder agreement in place so that the compan doesn't explode during takeoff :-)
In California, it is $800 or an amount based on total revenue, whichever is greater. The formula differs for LLCs, S Corps, and C Corps. Furthermore, S Corps do not pay the franchise tax in their first year unless they are profitable.
Generally, incorporation as an LLC is preferable for entities making more than $100,000 in revenue, while an S Corp is preferable for lower revenues.
If you're someone with lots of ideas and lots of peaks of excitement, it actually might better to postpone incorporation until you can't responsibly continue without some sort of limited liability.