My Gymboss interval timer is my partner in crime. I use it for HIIT (High intensity intrval training) training on the vertical bike. Instead of spending an hour doing cardio, I do my cardio in 20 minutes! This saves time and allows me to focus on my weight training. After 20 minutes of HIIT cardio, I'm dripping wet and burned just as many calories as if I did 1 hour of cardio.
I bought mine off their website for $19.99 plus shipping. It keeps me in tune with my intervals!