I find the best way to make CV less boring at the gym is to actually work hard and dont do the same thing all of the time.
I see many people who simply just go on the cross trainer for 30 minutes and then go at a steady pace and barely even break a sweat. Whats the point?
At the longest, my CV sessions last 50 minutes, usually less (40), and I work as hard as possible. I'll often do something like the following:-
8 minutes on the bike on the interval hill setting or personal trainer aerobics settings
8 minutes on the summit trainer, interval hill setting
8 minutes on the tread mill, running as hard as I can for that time
8 minutes on the rowing machine, rowing as hard as I can for that time (approx 2000m)
8 minutes on the cross trainer, aerobics program
If you work hard enough you wont have time to be bored, trust me. If you finish and your not trembling and feeling high from it you havent tried hard enough!
Including myself, out of all of the people I see doing CV, I would say a relatively small proportion of the gym goers at our gym simply dont work hard enough to make themselves any fitter. They are locked in that "must go at a pathetically low 65% heart rate to lose fat". Fair enough that will help lose some fat, but it is extremely boring, and it wont make you as fit or lose as much fat, or put on as much muscle than if you really work hard. In those cases you may as well just go for a walk or have a kick about with your mates.
I have noticed more of a change since I adopted interval style anaerobic training as my CV work in terms of muscle than I ever did taking it steady.
I'd suggest that if someone is bored with the routine of an hours steady cardio, then they should try working twice as hard for just half an hour. I bet them they will feel like they have worked much harder afterwards, and been less bored.
Just my 2p