A good source for tools, books, and info is Brownell's Gunsmith Supply:
http://www.brownells.com
There are a variety of types of engraving ranging from the "real" engraving where hardened gravers and small hammers are used to actually cut tiny grooves into the metal, to modern laser "engraving".
There's also acid-etch work, punch-work, and machine engraving.
The top-of-the-line Master-class work is inlay-work, where precious metals are embedded in the steel, then carved and engraved.
Tooling ranges from those small gravers and hammers to modern powered rotary-hammer tools like the "GraveMeister".
An excellent book showing some of the finest engraving ever done is the book "Colt: An American Heritage" by R.L. Wilson.
Wilson's book shows engraved Colt pistols done in a wide variety of styles from the 1830's to the late 1980's.
This is available from most book sellers, and is well worth the price.
In the gun world, World-class Artist-engravers sit pretty much at the top of the heap.
