The best place to start is Craigslist, where employers frequently post short-term job openings. You can also pick up gigs or advertise your own services for free. Beware scams, and don't give out personal information until you've met your employer and are certain the job is genuine.
Temporary agencies are another excellent way to find no-strings-attached winter jobs. If you have decent typing skills and are familiar with Word, Excel, and Powerpoint, you may be able to get a job--or a series of jobs--that pays substantially better than retail. Sign on with as many agencies as you can to increase your chances of getting steady work. Some major staffing agencies are Manpower, Kelly Services, OfficeTeam, and Elite Staffing.
Holiday Jobs at SimplyHired
Calls for holiday help across the United States.
About Winter Break Jobs
Monster.com Career Advice: Cool Holiday Jobs
Unusual retail jobs that don't involve working behind a counter or stocking shelves.