Concept 2 Rowers are hands down awesome for overall conditioning. Many mixed martial artists use them and looks like crossfitters caught up on to the benefits too. If you ever tried an "all out" 500 row, you definitely know what I am talking about.
This workout is very simple. You row 500 meters, then you take 2 or 3 minutes of rest and you repeat this for 5-10 rounds. Start slow. Try starting with 3-4 rounds and add a round each week and slowly build up. This workout will take your competition to the next level.