Over the years my regular gaming group has oscillated between using and not using critical hits tables. Our original tables dated from the late 70s/early 80s and were type-written copies from The Arduin Grimoire. Later we expanded these tables with new entries, and finally created multiple tables linked to various damage types.
As a quick project I've taken our latest incarnation of these tables and created a web-based and system-agnostic version. You can find the beta version right here:
Enjoy, and don't die!