April Cardio Challenge

It's a new month with a new challenge - Cardio Challenge.  The challenge for this month is to do at least 5 days of cardio for 30 mins of more.  Who is on board?  Getting that cardio in with help shed the unwanted weight and fat.  Today I completed an hour of bootcamp and then went for a 20 minute bike ride.  What are some of your favorite cardio exercises?