For me the best way to get unstuck is to go for a walk outside the office and think in peace. I work for a small company and we all share a working space so the distractions are endless... Either someone's talking loudly on the phone, or they're asking me questions (and the headphones, for some reason, do not work as a do not disturb sign for my coworkers) so at times it's impossible to concentrate...
When I'm working at home on my own projects, usually on the weekends, I go for a brief swim at the beach. It works wonders....