PFI Smokecap Silencer 

Yet another interesting airsoft accessory has surfaced. The PFI "Smokecap" silencer unit produces muzzle smoke for each shot fired. While not practical, the effects are visually appealing. The unit uses disposable smoke cartridges. Each cartridge lasts roughly 6,000 shots. There is no info on the pricing.

There is a video of the unit in action at the source link for those who are interested. =)