Goto http://www.ussafety.com/
Click on "Respiratory"=>Air-Purifying Half mask=>Series 100 Premier Silicone

This isn't exactly the model I have but I bought mine 10 years ago.
Silicone is good because it stands up well, is easy to clean and even
paint won't stick to it.  I got it because I do some TIG welding and
plasma cutting in my home shop.  Both these activities generate ozone
and we all know about that.  I'm also allergic to grasses so I wera it
when mowing the lawn on our garden tractor.  The filters I use are
activated carbon cartriges with dust filter pads the go on the front of
the cartridges.  I have replaced the dust filters (cheap) a few times in
the ten years and the cartridges only once and that was recently.  The
trick to that longevity is that after use I let the whole thing dry out
for a while and then double bag it in two plastic bags.  This keeps the
cartridges from slowly absorbing traces of stuff from the air and
shortening their life.

It never ceases to amaze me how effective it is.  e.g. If I lift the
mask away from my face to scratch my nose when cutting grass, I can
immediately smell the grass.  Similarly when spray painting.  But no
smells when the mask is in place.

Ted

The basic problem is that a half-face respirator will not do much
good.  They cannot get a solid enough seal and will only reduce your
exposure down to 10%.  

This is why you always see professionals (military, firemen, police
etc.) using respirators that cover the whole face.  (Which reduces
exposure to 1/50th.)

And I seriously doubt that anybody would let you onto an airplane if
you are wearing one.

"The commander in the field is always right and the
rear echelon is wrong, unless proved otherwise."
  General Colin Powell