There are basically only two kinds of rolls that I know of, Gymnastic/Tumbling rolls, and Martial arts/Parkour(they are almost, but not quite the same) rolls.
In tumbling forward rolls, you roll straight forward, going directly over your head and the center of your back. You can’t really aim them in any direction, and they aren’t really useful in any situation where Parkour or martial arts would apply. (I.e they may be an important part of a gymnastics or tumbling routine but they aren’t going to help much the next time you jump off a wall or get into a fight). For backwards rolls, well I can’t really remember how to do them, but their pretty similar to forward rolls.
In Martial arts forward rolls, you roll at an angle going down your arm, over your shoulder, and across your back, so that the least amount of time/force is placed on the spine. You can aim the roll in any forward directional without moving your footing once you know how to do it. (I.e you can roll side ways, diagonal and forwards). It’s all the same roll. Martial arts rolls are meant to be used to dissipate the impact from a fall, or to recover from being knocked over, or to land from being thrown, either in an accident or fight. Back rolls again are similar, although I don’t know them as well, in a back roll you fall backwards and roll across your back and over your shoulder in reverse.
Now keep in mind, I’m just listing the different types of rolls here, not how you should do them. Also, I don’t really know much at all about tumbling rolls, I haven’t taken gymnastics in a while.
Here are some examples of rolls and how to do them.
http://www.youtube.com/watch?v=F7b-ykpV … 40&index=0
Martial Arts forward rolls
http://www.youtube.com/watch?v=ooH61uam … 40&index=1
Same in slow motion
Parkour rolls (I’m dubious about his expertise though)
More parkour rolls, I like this video better.
Finally! This video kicks the other two videos asses, reminds me of watching dogens tutorials for the first times, must be the pleasant background music. Watch this to really learn practical Parkour rolls!
Now, I couldn’t actually find any videos of Gymnastic/Tumbling roll, aka a somersault. If you want to see one, just search gymnastics, or tumbling or something on youtube, and watch some videos of the Olympics or some such, you’ll see some rolls somewhere in their floor work.