A S-Corp is easier to convert to a C-Corp, so if you want to go the VC/IPO direction, but want to start simpler, you might want to start with an S-Corp. http://www.feld.com/wp/archives/2006/02/s-corps-vs-llcs.html

But an LLC is more flexible and generally simpler to start.

If you're looking to build a small profitable company, I'd go LLC. If you're looking for VC money today, go C-Corp. If you're looking to build a profitable company but want VC money in a few years, consider an S-Corp.

Talk to a lawyer and accountant, of course.