While previously mentioned Fluid is a great tool for creating site-specific browsers (SSBs), some people really like Chome's "Application Shortcuts" feature. Unfortunately, it's not available on the Mac version of Chrome, but you can achieve the same result with a shell script.
Software blog The Less Annoying Blog has written a shell script just for creating SSBs that run on Google Chrome. Just download this script (a very slightly modified version of the original) and save it somewhere permanent, like a scripts folder in your Documents.
Next, open up Terminal and run chmod +x filepath, where filepath is the path to the script. This will make it executable.
Now, whenever you want to make an app shortcut, just drag that script into a Terminal window and hit enter. It will ask you to name the app (unfortunately, the name doesn't allow for spaces), specify a URL and choose an icon, which you can get easily from Google Images or the Fluid Icon Flickr Pool.
After that, head into your applications folder and you'll find your new application shortcut there. If you double-click on it, you'll find it opens as a separate application in its own little window and with its own dock app. Note that any Google Chrome preferences and extensions won't carry over, since this creates a new Chrome profile for each SSB. So if you need to apply user scripts or anything else to that site, you're probably better of opening it as usual in Chrome or using Fluid to create the shortcut.
Create Application Shortcuts in Google Chrome on a Mac [The Less Annoying Blog]