The single greatest resource I have access to in my profession is the Institute of Physics’ (IOP) discussion forum. Any query I have ever had has been satisfactorily answered. It works because it has a large critical mass, although like most forums most members are happy to just read, which is fine too. I imagine this is partly due to lack of confidence, which would also explain why similar forums here are not as successful.
Nevertheless, if you reading this as a physics teacher you could do a lot worse than join the PTNC Phyics discussion forum.
While you’re at it why not join their Schools & Colleges Affiliation Scheme? You get a monthly magazine/journal (called Physics World) which keeps you up to date with latest developments in physics, and it’s pitched at just the right level for teachers. There’s also their Physics Education monthly journal, and they offer lots of resources like posters and DVDs, which make a very pleasant surprise when they arrive in the staffroom letterbasket.
Check out their schools and colleges page for an overview of what’s on offer, and make sure you watch the animations on the radioactivity page.
Money well spent I’d say myself.