Roger the GS over at Roles, Rules and Rolls explains why there is a dungeon under your city using real world examples.
Melan over at dragonsfoot dissects megadungeon mapping and adventure design.
The Welsh Piper talks about the problem with retroclones. I disagree with him a bit, but it's an interesting read.
EG Palmer over at Old Guard Gaming Accouterments posted a wonderful post about the types of thieves found in Wyrd Greyhawk. You should definitely take the time to read this, especially if you're planning on