A short post to mention this freeware application (for Mac) called Disk Inventory.
The nice thing about it is the visual representation of the disk usage on your hard drive. As you can see from the picture, Call of Duty is currently occupying a largish chunk of hard drive.
Numbers will tell you the same thing, but a picture tells the story better - although I can get the same information on disk usage by checking the directories, the picture at left helps me zoom in on what's really taking up the most space on the drive.
Now, to see what that blue chunk is ...