If you want to get a good argument started, put a couple of hack and slash DMs in the same room with a couple of role-playing DMs and ask them what do they think of riddles in D&D. The Iron DM opinion is that riddles are great when put into the context of the adventure. Just as there is no single roll to win a combat, (which tests the combat tactics of a player), there should not be a single roll to win a mind test of the players (which tests the adventuring tactics of a player).
101 Riddles, published by Stainless Steel Dragon and written by Jon Volden is written for the Dungeon Master that relishes in sending his players through a challenging ringer. The PDF contains 101 riddles for words and phrases typically encountered in an adventure.
The 46 page book is well bookmarked, though the layout could have used some work to save white space. The riddles themselves are not too difficult, nor too easy. They are also quite unique. The book’s biggest problem is that it itself is too simple. It is a simple book of adventuring riddles. The hope would be that it would have added 1 or 2 implementation ways as previous similar supplements have done. Providing things like recommended hints for the riddles would have helped evolve the book to the hack and slash crowd.
For the Iron DM
This is one of the best collections of riddles you will find. They deal specifically with things you will find in a typical campaign world. I was particularly impressed with the seven sin riddles.
The Iron Word
101 Riddles is a great value, providing 101 mind puzzles for your players, though be warned that there is nothing included in the book to help facilitate them in your campaign.
[3 of 5 Stars!]