Brad wrote
Microstamp in Pasadena, CA has been mentioned several times on this list. I visited their shop and was impressed with the variety of what they can do, literally anything you need. But I found their prices for a simple text stamp were a little steep.
I bought a simple text stamp from Microstamp… apparently didn’t do
much price shopping at the time. 
One unexpected benefit is I
believe my stamp was made from stainless steel. All my quality
marking stamps can rust and corrode like my other steel tools, but
this stamp is as bright, shiny and crisp as the day it arrived. I do
have to question whether it is indeed stainless because I thought
that would be a little soft for a stamping tool, but maybe since I’m
working on non-ferrous metals it is hard enough.
It is a high quality tool I expect to last me a lifetime. I’m sure
there are other good ones out there, but I don’t know if you can get
a better one.
All the best,
Dave
Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com
http://www.CarolinaArtisans.com