My impression is that in the US, there is a canonical place for finding math jobs, namely mathjobs.org. For those of us who live and apply for jobs elsewhere, life is more complicated, and searching for advertised academic mathematics jobs for example in Europe can be a real hassle, with loads of different sites, different systems, and some jobs apparently advertised only on the web page of the hiring institution, or one some obscure mailing list.
So, where are academic math jobs advertised when they for some reason are not or cannot be on mathjobs.org? Of course I know of a few such places, but I am sure there must be many more.
All answers welcome, this would help me and probably many others.
Edit : All answers are 10 years old. Some of them might not be working. Any new answers (or corrections to old answers) would be useful.
Best Answer
Actually, the canonical place for finding math jobs in the US is the AMS Employment Information page. This is much older than MathJobs.org, and I still think notably more complete for more obscure jobs (and actually has quite a few foreign jobs), though MathJobs.org adoption is moving fast.
EDIT: As noted below, in the time since this answer was written, EIMS is being discontinued, and essentially replaced with MathJobs.