Freelancing is a great option, as it will allow you to utilise the skills you are likely to have
gained by creating a startup, while also giving you the opportunity to work on a contact-to-contract basis and it can be immediate (for $1000 anyway).

I run an online freelance marketplace for experienced professionals called Expert360.com. Our online workplaces empower businesses and freelancers to come together regardless of where they happen to be, to get work done. If you create a consultant profile, you can view projects and apply for relevant pieces of work. A number of the companies in need are start-ups - so perfect :)
Good luck!