The idea of gorgon as a petrifying armor-plated bull has interesting possible origins. One theory says that Hetrodotus originally wrote about the fantastic african beast, the Catoblepas (Yep! You read that right!). Then the greeks eventually folded that in/confused it with descriptions of the rhinoceros and named the resulting folklore after the Medusa-style gorgon for its stone-turning ability.
Whatever its genesis as a classic D&D monster, I don't see gorgons come up too much in games (despite my having a mini for it!). Maybe it's the naming confusion. I don't know. It does show up as a wandering encounter in dungeons (Levels 6-7), and a few terrain types. Rare or not, it's a nasty thing to throw at PCs.
Gorgon (from Cook)
No. App: 1-2 (1d4)
Move: 120' (40')
Attacks: 1 (gore or breath)
Dmg: 2d6 or petrify
OK, first off this thing is physically pretty tough. Its scales give it plate mail-like protection and it has up to 64 hit points. In other words, it's not going down easily.
Its horns do respectable damage, and it gets to double that if it charges. Let's get real, though, the breath weapon is the moneymaker here.
As mentioned previously in this blog, petrification is a scary thing for PCs. Players, as a rule, hate it! The vapor covers a 60' long by 10' wide area and the gorgon is immune, so it might "ground zero" itself and catch any or all nearby PCs. Another tidbit, there is no listed limit to how many times or how often the gorgon can use this attack! So the odds are good that someone is ending up a lawn ornament (at least temporarily).
On the downside for this thing, it doesn't have a great morale and most versions' monster listings peg it at animal level intelligence; so you might drive it off. It has fairly decent treasure (type E), so it can be worth a party's while to track it back to its lair, but remember the number encountered in lair is up to four, so watch out!