Now there's a somewhat obscure stat that doesn't get a lot of publicity (outside the world of catchers).
Here's some info published by Chuck Rosciam of SABR:
When a runner attempts a steal, “… the result is either a caught stealing by catcher (CCS) or stolen base against the catcher (SBA). The odds are in favor of the runner (70% success rate during the period 1980 – 2002). Therefore a catcher having a better rate than catching 30% (MLB average) would score better than 1.00 if the formula for a good arm is:
CCS/(CCS + SBA) * LgCCS%
...where LgCCS% represents the league average success rate
Hope that helps.