The GL2 has a mini-plug microphone input. This limits your options. You can use the R0DE VideoMic, which is a pretty decent value for $150. It can be used on-camera mounted on the shoe, or you can put it on a boompole. It will sound better than your current on-camera mic. The downside is that if you put it on a boom, you really shouldn't use more than a 10 foot cable to run it to the camera's mic input. Also, some people don't like that the VideoMic wobbles a little bit. The mic is floating on a shockmount, and it tends to sway back and forth a little more than it should.
If you wanted to invest a little more money, you can get this adapter:
http://www.bhphotovideo.com/c/product/256059-REG/Canon_8032A002_MA_300_Dual...
That gives you two balanced XLR inputs. With that you can use professional shotgun or multiple wireless mic systems.
