I just looked it up and the smallest I could find was a Trimma Goby. It gets up to 1". The second smallest one I could find were the Clown Gobys. They get to a total length of 1 1/2". The only clown goby that doesn't fit into the 1 1/2" catigory is the Citrinis Clown Goby they get up to 2"
The neon goby gets up to 2"
The rainford's goby gets up to 2 1/2". Below is a pic of my rainfords goby just to give you an idea of what they look like. (really cool little fish)
What kind of prodject are you working on?