It depends a lot on what you're doing. Things genuinely close to the bleeding edge of technology often get DARPA funding, and the list of DARPA alumni companies

It depends a lot on what you're doing. Things genuinely close to the bleeding edge of technology often get DARPA funding, and the list of DARPA alumni companies is pretty long - even for stuff that at face value might not have military applications. But what most people think of when thinking about the "startup scene" is mostly private VC funds. There are various other small business grants from federal and state governments, but they're generally dwarfed by the private investors.