I backed this item as a kickstarter, but it combines all the things you need - a marker and eraser all in one. Just add in your favorite dry-erase marker (I like expo markers the best) and you can write with it and have an eraser handy. Better yet, it is magnetized, so it will just stay where you leave it on your board!
Wrigo Mag 2-Pack*
Expo Markers*
Wrigo Mag 2-Pack*
Expo Markers*