For academic positions in Europe, start with the profiles for Careers by country compiled by the European University Institute.
Other sites for jobs in colleges and universities may be found on the guide to Careers by Category: Teaching & Academic.
Many companies do not list their job openings on the national sites such as Yahoo! HotJobs and Monster.com, but on niche job boards, some of which are run by professional or trade associations. Sites that focus on specific industries or occupational categories include: