Hi, unfortunately I have not found any device that works; there is an app 2screens that allows you to control the presentation using an iPhone via bluetooth, the bad issue is that you have to export the presentation (keynote or power point) into the iPad aplication and will lose transitions and animations, the good issue is that on the iPhone app you will have a little image of the current slide and a timer. The iPad app also have the option of make a drawing over the slide or use a white blackboard to write on it.
I am still waiting to have a device like the one I used to use with my netbook or the possibility of use keynote remote on the Iphone to control the iPad.