Professional Organizations
Many professional organizations have their own job lists as well as resume building workshops and mentor programs. Find the organization that best fits your career goals and check their website. Some allow you to sign up for email alerts for new job postings.
Popular Job Search Websites
Check specific institution websites. Some smaller libraries may not be able to afford the fees of posting on the larger sites. Same goes for businesses. They may not realize that they need someone trained in library and information science and do not post on library-specific job lists. Use popular sites such as CareerBuilder, Job, Indeed.com, LinkedIn, etc. and search for "information," "research," "archive," and other information organization terms to find these hidden job postings.
Listservs
If you go to school for library and information science, your school may regularly email job postings they have received.
You can also join a list to get emails and see conversation about a sub-area of librarianship. Occasionaly, you'll also see job postings through these servs. Here are a few:
This issue of American Libraries (the magazine of the American Library Association) is all about the job search. The Special Report is Good Job Hunting (pages 26-45) and contains articles on resumes, negotiating salary, advice at different stages in your career, HR tips, networking, unions, and potential barriers in the job search.
A Good Match by 
A Librarian's Guide to an Uncertain Job Market by 
What's the Alternative?: Career Options for Librarians and Info Pros by 
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