Tetra Whisper Air Pump (Non-UL) by Tetra.
Of course this is intended for use with an aquarium. Homebrewers use similar pumps to aerate wort. Aeration can help reduce lag times, encourage yeast cell reproduction and produce more vigorous fermentations.
Typically you would use both an aeration stone and an inline filter along with this.
Update: Since this post was published the price, availability or promotion has changed. Check the product page for current description, price and availability. Also: Today’s Deals on Amazon
More: Recent Amazon Finds
Oxygenation and Aeration Supplies at William’s Brewing