I was just doing some research on yo-yo loaches and Fishy Friend mentioned two loaches to check out- Zebra Loach and Dwarf Chain Loach. Zebra Loaches look like they get about 4" and Dwarf Loaches look to be much smaller around like 2".
Skunk Loaches are also quite small at about 2". However, be warned, these skunk loaches are pretty aggressive despite their small size. Very cool fish, but they are like tiger barbs, they can really harass other fish in the tank.
Dwarf chain loaches are the smallest I know of. Some species of kuhli actually get quite large, up to 6" from what I hear. Dwarf chain loaches stay around 2" or smaller. Cute little buggers, too. I did love mine, though I only had them a short while.
I would say Zebra, but they may very well be the Dwarf chain loaches that June mentions. At any rate, they get to only about 2 1/2 inches, and, like the French and me, eat snails. They are not so fussy about the sauce, either.-rick