If you're looking for opportunities to work in the USA you'll need to do your homework first. The USA is very strict about who they let in to work, and the visa laws and requirements are also quite stringent. You need either a green card (almost impossible unless you've been living and working in the USA for a while), or a Legal Sponsor for the visa.
The most popular visa for students and young people is the J1 Visa. There are a few companies that will work on your behalf for a fee, and some will help you to find a placement too. You CAN'T get a J1 Visa without going through one of these organisations.
The most popular kind of work for gappers in the USA is spending a summer at a kid's camp, as this is open to anyone between the ages of 18 and 30. There are plenty of companies that will help you find a camp placement and provide the necessary sponsorship for you to go and work at a summer camp. In return they get some cold hard cash, while you get a small amount of spending money and an awesome summer in the States.
If you are a university (or equivalent) student then you can also look at casual summer jobs. Companies like IST Plus and Real Gap offer opportunities to experience a whole range of epic jobs in America via sponsorship. Current favourites include working at the Maryland Zoo or at a beach club in Orange County.
You can also look into working in the USA as a
If you are looking for an internship during or after your degree, then you can also apply for the J1 Intern or Trainee. This allows you to work for up to 12 or 18 months in a job related to your field of study. Having a sponsor for this programme makes it a lot simpler for US companies to take you on.