I get that from time to time as well and it's very annoying, especially if you only want to watch a simple trailer for the new series of BSG. Region coding of DVD's is one thing but blocking access to free online trailers by geographic location is bordering on the ridiculous.
Timeless has the right solution though, it is possible to setup your browser to surf through a proxy server, just be aware that this is not an ideal solution. Most free proxy servers are only designed for limited use and not streaming video, you may require a commercial one to get the best performance. Proxy's can also be banned from some sites and servers as they have sometimes been used by hackers for abuse.
The alternative method is to spoof an American IP, but that borders on hacking and I’m not inclined to indulge. Sometimes also changing the region of your computers operating system (OS) will work too, it just depends on whether they check your location by IP or OS data and sadly it’s usually the IP.