If you are a foreigner in the USA with a standard non-immigrant visitor's visa, you are expressly forbidden to partake in paid work and will be deported if you're caught working illegally. Employers are required to establish the bona fides of their employees or face fines, making it much tougher than it once was for a foreigner to get work.
To work legally, foreigners need to apply for a work visa before leaving home. A J-1 visa, for exchange visitors, is issued to young people (age limits vary) for study, student vacation employment, work in summer camps and short-term traineeships with a specific employer. One organization that can help arrange international student exchanges, work placements and J-1 visas is International Exchange Programs (IEP), which operates in Australia (www.iep.com.au) and New Zealand (www.iep.co.nz).
For nonstudent jobs, temporary or permanent, you need to be sponsored by a US employer, who will have to arrange an H-category visa. These are not easy to obtain, since the employer has to prove that no US citizen or permanent resident is available to do the job.
Seasonal work is possible in national parks and at tourist attractions and ski resorts. Contact park concessionaire businesses, local chambers of commerce and ski-resort management. Lonely Planet's Gap Year Book has more ideas on how best to combine work and travel.
Au Pair in America (www.aupairinamerica.com) Find a job as an au pair in the USA.
Camp America (www.campamerica.co.uk) Offers opportunities to work in a youth summer camp.
Council on International Educational Exchange (www.ciee.org) CIEE helps international visitors find USA-based jobs through its four work-exchange programs (Work & Travel USA, Internship USA, Professional Career Training USA and Camp Exchange USA).
InterExchange (www.interexchange.org) Camp, au pair and other work-exchange programs.