A lot of the best shirt designs in this world catch the eye with their simplicity and inspire the imagination with the story told by their imagery. I found both of those elements to be present in GrafikNoise's SoundSeries.
For me, a lot of the fun is in the juxtaposition of these still, silhouetted images with action sounds. It gives the feel that something is about to happen. The large type size for the sound also gives each piece an exaggerated importance, which (especially in the case of the mouse) adds some humor to the composition.
Another element of the site that I really enjoy is the color options- each design is available on multiple shirt colors. It might seem like a small thing, but it adds a lot of appeal (especially for people like me, who have developed a recent fondness for pink shirts and suddenly can't find any decent ones anywhere).