I haven't personally used one, but try searching for affiliate job board widget. Monster has one at http://publisher.monster.com/Widgets/ for their affiliate publishers. See these links:
http://publisher.monster.com/
http://publisher.monster.com/Widgets/Job-Board-Widget.aspx

There are others. Either search for affiliate on major job boards, or do the search I suggested. You can also see these widgets that came up for a search on widgetbox for jobs: http://www.widgetbox.com/search?q=jobs

The key thing to know is that you want an affiliate plugin or widget provided by a major job board that has many listings. It would make sense for LinkedIn to have an affiliate offering for their jobs listings; however, I haven't found information on it yet. If I don't find it fast enough I won't be able to edit this answer to include it. You can contact me for more details on these.

If you find one you like or need additional information I can ask our Blogger Mastermind group if anyone has used any of these or can recommend others. We have 100+ serious bloggers who are likely to have more suggestions.

If you are wanting to leverage a third party job board, I suggest you look at http://blog.jobamatic.com/2010/02/setting-up-contextual-widgets.html. If you are wanting to have your own job board, leveraging an open source job board (there are plenty looking at the results of https://www.google.com/search?q=open+source+job+board and http://www.jobboarddoctor.com/resources/job-board-software/) that include widgets or let you build your own is fairly straight forward.