Most chalk markers work great and are easily cleaned off! For best results, clean the marker off within 48 hours.
When cleaning, I like to use a wet rag and dry rag. Wipe the writing with the wet rag and dry as you go. Otherwise the writing smears all over the board and is harder to clean. Take care not to get marker on the ruler frame while you're cleaning, it will stain!
Stubborn chalk markers can usually be cleaned off with a magic eraser. Avoid using metallic color chalk markers- they are similar to paint and don't erase well.