Near rhymes (similar sounds, but not perfect):
* Hardboard
* Keyboard
* Award
* Sword
Eye rhymes (spelled similarly, but pronounced differently):
* Board
* Chord
Creative options (playing with the meaning):
* Thought word (referring to the content displayed on the board)
* Portward (if you're using the board for presentations about shipping)
Ultimately, the best rhyming word depends on the context and the intended meaning of your rhyme.