This is an Otocinclus. They are sucker fish, who like algae and swim quickly. They're very hard to catch. Otocinclus, at least the dwarf kind, get to be only about 1 1/2 inches long. This one is probably an inch at the most right now. S/he is sucking on the inside of the tank. I took this shot from the side of the tank looking out the front. The one on the left is him/her. ;) (duh.) S/he's got two reflections, for some reason.
For those who've been wondering: Yes, the plants in my tank are silk plants. I can't stand the plastic kind, and the real ones get mauled by the critters, so I went with fabric. :)
I was going to wait and see if I got a better shot later today, but got bored this morning, so decided to try to photograph the fish again. Eventually, I'll be able to get a shot of the Zebra Danios! They swim just as quickly as the Otocinclus do, but the Otocinclus do tend to stop for a while, occasionally.
I'd also like to get a shot of one of my Neon or Cardinal Tetras, but the flash just makes the colors on them explode and it looks like the pic is blurry when it's not, it's only the reflections shooting every which way.