Knog have designed a rather nice and unobtrusive looking bicycle bell, called the Oi:
Unlike a conventional dome-shaped bell, it takes up only a thin strip of handlebar space, and every part of it sits close rather than sticking out. Also, while this feature might be more applicable to road and commuter bikes with narrow bars, it even has a clever bit of cable management built into the clamp:
Here are a load of the prototypes they went through:
At present they’re only available through Kickstarter with delivery expected in August this year. Since they’ve raced past their target in a matter of hours, we expect to see them for sale by more conventional routes subsequent to that.