I have Spinervals, iTrains and Cardio Coaches - there are things to be said for all three. I think they are all good, actually.
Spinervals have been around for a long time - Coach Troy knows his stuff and if fun to have coach. The main benefit of the Spinervals is that, like doing a Cathe video, you don't feel alone - there are others working out "with" you on the TV and if you "zone" out like I do when I spin, you can quickly figure out where you are tension-wise by looking at the screen. The big downside to them is that they are DVD's and are expensive. I love climbing hills and I have Spinervals Hillacious - it's a tough, fun hour long workout, but it is all hill work. Spinervals is also a true interval workout with rests (soft pedaling) between pushes.
Cardio Coach is the audio version that's closest to Spinervals. These, too, are true intervals and are of varying lengths and intensities.
iTrains are more like a traditional spin class with varying intensities and speeds. They are also fun and tend to be the cheapest of all of them. Both Cardio Coach and iTrain are downloadable MP3 files - you can burn to a CD or save to an iPod or MP3 player.
