diablo-3
After reading about Development Hell and the unburied Jay Wilson, I happened to stumble upon the Quality Well (on Nightmare) whilst clearing out Old Tristram. Upon my decent into the dark murkiness of the well, I found it populated by all manner of foul, lurking beasts: Blizzard QA zombies.
Is there any other purpose behind the Quality Well, other than to show off the undead QA team?
The complete details for each gem type and quality level appear on the official guide: http://eu.battle.net/d3/en/item/gem/
In short:
Helm Weapon Other
Amethyst +%Life +Life per hit +Vitality
Emerald +Gold +Critical Damage +Dexterity
Ruby +XP +Damage +Strength
Topaz +MF +Thorns +Intelligence
+MF means Magic Find.
You can typically tell what gem is present in an item by looking at the shape of the gem, though it is shrunk somewhat on the gem image within the socketed item. There will be some that are hard to tell - every "refined version of the previous shape" level is going to be hard to tell apart when shrunk down.
The mod of each gem placed in a socket will be shown on the item, so you can derive exactly what's in that socket by looking up the mod. For example, I've got two +18 Int gems in the following, which I can look up to be Flawless Topazes on the Gem site.
Best Answer
Nope - just a secret joke dungeon. Rumor has it that if you're particularly unfortunate, you might stumble across Development Hell, as well.. (I know you mentioned it, but seriously. Development Hell. It deserves a second mention.)
Oh, and you might also find Bashiok lurking around the Oasis in Act 2. If you've got Rakanishu's Blade, he's even worth an achievement.