I checked out the basics like monster, and craigslist (though that is city specific). If there’s a specific field you want to get into look up organization or societies for that field. For example I wanted a forensics job so I found the AAFS (American Association of Forensic Science) and they had an employment resources section on their website with a list of posted jobs from around the country.
A fall back, my last one, was to simply type in the type of work I wanted to do (so for lab work, laboratory) and the city I wanted to do it in. Then I would go down the list of labs and their websites and check the careers sections.
When using sites like Monster be sure to try going to the companies actual website separately. A lot of times the job sites use convoluted methods of getting your info back to the company.