I was a big fan of the original Treo 300 soft case.
I'm often scampering around on steep rocky slopes
and needed a case that would hold the phone securely
and keep the screen safe under all circumstances,
including running, jumping, or pushing through heavy
brush and scrambling over rocks, and occasionally
falling down.

I liked that case so much that I used it for
the Treo 600, which has the antenna on
the other side, and is a lot narrower, so it wasn't
a good fit, but it still let me carry the phone
screen inward. The velcro finally wore out and
I've been looking for a replacement for about a year,

Imagine my surprise when I'm looking for some parts at
Ace Hardware and spot the perfect sport/utility case.
Nite Ize small clip case. http://www.niteize.com/ClipCase.html

Some photos.

The sides are made of slightly stretchy material so it
holds the phone snug, but also has some little pockets for
a pen and such. One little bit on the inside I didn't care for
so I snipped it off. It's a little thicker than some
other cases, but offers superior protection so it suits my
needs. I figure this one may wear out some day so I
bought two, just in case.