What are the most common ways to find open postdoc positions in physics, in Europe? I use inspires and academicjobsonline, but on both sites, there almost haven't been any new positions in my field (4 in total since december). Are there any other sites / tricks I'm missing?
(EDIT: my subfield is theoretical QCD)
Many jobs are only advertised on the website of the respective universities. Often professors post positions on their home pages or group pages, so it may be a good idea to keep an eye on them. Sometimes job openings are also mailed around to colleagues, so it is a good idea to let people know you're on the market, so they can forward these announcements.
Depending on your particular subfield there may be other relevant websites as well.
Perhaps you should also look at http://jobs.physicstoday.org/jobs/work_function/postdoctoral-research , http://www.jobs.ac.uk/jobs/physical-and-environmental-sciences , http://www.eurosciencejobs.com/jobs/physics , and http://jobs.sciencecareers.org/jobs/europe/postdoc/ .
From my experience, most postdocs in high-energy physics have application deadlines anywhere between the previous September and the end of December. That is, for postdocs starting in fall 2014, you need to be filling out applications in September-December 2013. At this time of year, though, there are just not many people listing open positions. It's not just you; I've been looking at the listings as well and very little has been posted since the first week of December.
Open positions in public institutions often will & have to be announced on a public job database, not so likely on private job databases where you find mostly industry positions (e.g. in Germany, Austria, Switzerland, Netherlands).
Often higher academic positions are listed in printed newspapers in Germany.
Another option is to look on the sites of the national phyiscal societies (e.g. http://www.pro-physik.de/phy/stellenmarkt/jobsHome.html)
In this answer I gave some tips how to find websites of research groups specializing in field X, you can add here "positions".
There are various listings of jobs and sites where open positions are advertised, for example
http://de.physnet.net/PhysNet/physjobs.html
The sources listed in other answers are also available. For your field, there is also the HEP Postdoc Rumor Mill
https://sites.google.com/site/postdocrumor/
that should be starting the 2016 version before too long.
