When I lived in Holland, I bought a little device for my Gazelle opafiets that really helped when I had to carry the bike up or down stairs. It was a spring about the size of ones finger that mounted to the underside of the downtube just behind the headtube on one end, and to the back of the top of the forks at the other. Basically, a steering stabilizer. The spring's torsion kept the forks pointed straight ahead unless pressure was applied to turn the handlebars.

Unfortunately, not only can I not find them here in SF, I don't even know what they're called. Anyone know what I'm talking about or where they might be found?