Arby's Reuben (review) features sliced corned beef, Swiss cheese, sauerkraut, and Thousand Island dressing on toasted marble rye.
Additionally, Arby's is offering $1 upgrade charge if you want to upgrade your Reuben, alone or in a combo, into a Double-Stacked Reuben (it comes with double the meat; I tried that too). The $1 upgrade runs all month long.
They also have a Facebook offer on their Facebook page, where you can get a free small fry and drink with the purchase of a Reuben. It's expiring soon though on March 11, 2014.