Working in a startup is different than any other job. It is the most fulfilling experience if you seek constant stimulation, a fast changing environment and if you can learn about anything in a matter of weeks.
I have spent my entire carrier at startups, small startups where i worked alongside the founder and larger startups that grew rapidly. When I joined Google in 2002 it was barely known startup with a few hundred employees – when I left in 2009, Google has 30,000 people working there.
If you want to join a startup, below is a list of the companies I funded and helped to start. Good luck!