As a cool alternative to traditional airstones you can use air curtains or air disks. 

Air Curtains are porous rubbery tubes with a wire core that lets you bend it into different shapes: snake it through your rocks or shape it round an ornament.  The bubbles stream out along the length.

Air Disks are flat and round like a plate, so fine air bubbles fizz out from the whole circular area, giving an overall effect of a jet stream.  They are supplied with 2 x suction cups to anchor the air line.

Curtains and Disks are both compatible with the standard air hose and can be laid on top of the gravel or weighted with a bit of plant lead and buried just under the gravel so it looks like the bubbles are coming out of the gravel bed.