I have two of them: the Proporta.com aluminium case (with neoprene
internals) and the original one from the Palm.
No one is ideal. The Proporta one offers unparalleled level of
protection ( its basically an aluminium shell) but it makes keyboard
use problematic as the rightmost part of keyboard is obscured by case
doors.
The Palm case is much softer an it front part can be rotated to the
back so it makes no obstacles during writing. It was probably ideal
when it was new. But today the material is old and the parts which are
designed to be bent became cracked and teared after the first use (my
case was never used).
Jynx suggested the Belkin case. But I will probably use these two which
I already have because the Tungsten W is not my main device (I still
prefer to use the old good III devices with their AAA batteries).