I was in a plateau from June 2012 till about October 2012 - stuck between a 3lbs range! I was running almost every day all summer. I then got a new workout Wii game in October and wouldn't you know, my weight started to drop again! I was so into my running routine that I didn't change it up. My body got to used to it. I was basically maintaining. I wanted to continue to lose so I had to change my routine. I "always" try to change my routine every 4-8 weeks depending on how my body is feeling.
If you like your machine at the gym, consider trying a new one. Trade the elliptical for a stair stepper, or the stationary bike for a treadmill. It'll give your body something new to do.
Don't go to the gym? Pick up a new workout DVD at the library, search for videos on YouTube, or buy a new one!