I was told that certain plane spotting activities like taking photos of aircraft taking off and landing could be illegal since 9/11? What are the regulations on this, and what should I be aware of before I set my camera up at the end of the runway?
Generally absent a specific prohibition you can take a photo of anything you can see with your eyes from public property (like a sidewalk). That includes airports, airplanes, bridges, tunnels, police officers, kittens, and unicorns.
So what constitutes a "specific prohibition" on photography? Generally a clearly visible sign that says
Absent such a clear prohibition you're free to take all the photos you want as long as you're on public property while you're doing it (i.e. "not trespassing on airport property"), but be aware that some law enforcement officials may not see it that way, and you may have to have some uncomfortable interactions with them.
If you want really good photographs (and you're not photographing at a major airport like JFK or O'Hare) you might want to speak to the airport management. At smaller airports someone - either airport personnel or a local pilot - might be able and willing to escort you airside where you can get some really great shots.
The ACLU notes that:
Popular among photographers, The Photographer's Right, a summary of legal rights related to photography (prepared by a lawyer), says that:
Some airports are more spotter-friendly than others. You can search online to find discussion forums on people's opinions which ones are better than others. Any airport that is private property (not many major ones, I believe) of course can do whatever they want, but many airports stop photography for a "safety" measure.
Standard IANAL disclosure.