This is the smallest one I know of. Many here use these successfully.
Internal Sponge Filter CAF-10
The Tetra Whisper 10 is a reliable, quiet, competitively-priced airpump. You'll also need a few feet of airline (silicon is worth the extra pennies), two T-fittings and a cheap air-adjuster valve from your LFS. And a back-flow check valve if your pump will be located below the water level.
Here's something about sponge filters: http://www.tropicalfishkeeping.com/b...torial-318602/
Alternatively, the Azoo Palm is a cheap reliable HOB (hang on back) filter with lots of room for media/foam that many members like.