Via Wandering Arameam, Amtrak is offering bonuses for Acela and Northeast Regional train travel through September 4.
Every 6 one-way trips on Acela earns 3000 bonus points (registration required) and the bonus can be earned three times.
Every 4 one-way trips on Northeast Regional service earns 1500 bonus points (registration required) and the bonus can be earned three times as well.