If you're searching for a job in Brussels those are the websites I recommend:
www.eurobrussels.com
jobs.euractiv.com
xpats.com/jobs
I had especially good experiences with the last website, since it is not that popular me and some of my friends managed to get interviews/jobs in embassies, permanent representations and other organisations working very closely with the EU institutions.
Also take a look at the EC Newsletter, sometimes they publish really interesting job ads:
http://groups.google.com/group/ec-news?hl=en