Telescoping seat posts

[Irulan]

"Gravity dropper" is the most common term. I also think that's one of the brands out there but people use the name like "Kleenex".
I love mine. You'd have to rip it out of my cold,dead hands. They aren't cheap though, if you put them on aftermarket. Figure $300 with install. You cannot use a seat bag with them.
I've always been a believer in "saddle down" for descending even in XC riding. I wore out two quick releases. And this is soooo much easier. :-) I think it will make you a better rider. Saddle down forces you to use your body correctly as the saddle isn't in the way.