Groddy Grout: Cleaning Tile Grout?

[ Photo by Danielle Blake ]

We have a tendency to get a little OCD when it comes to cleaning the bathroom. About halfway through the bathroom beautification process, we'll bust out an old toothbrush and go to town on the floor tiles (and sometimes the shower). But despite our best efforts, the tile grout still looks the same! In fact, one particular stain got us so worked up that we managed to pull a muscle in our back...

After popping two muscle relaxers and firing up the heat pad, we mused, "There's gotta be a better way to clean that...zzzzzzz..." Our tile grout isn't grimy enough to warrant a visit from a professional, but there's some stains here and there. Anyone have a solution or a product they can recommend?