I think that no Dungeon Master with just a little self-esteem should be without this book. The "Draconomicon" gives a comprehensive overview of the game's most fabled, respected and feared creatures. Finally it is possible to use D&D's namesake creatures in lower-level campaigns, so the players don't have to wait until they reach epic levels before catching their first glance at a mighty Red. Previously, it was virtually impossible to stage a "realistic" encounter between a low- to mid-level party and a hostile dragon. With the (please excuse the pun) scaled-down versions, the DM has a wide range of options at his or her disposal to give the heroes a battle their bards can sing about for the rest of the campaign. There's so much information about physiology of dragons, dragon hoards, age, abilities etc. in this book, it makes the "Draconomicon" a fun read - for PCs and DMs alike - even without actually being involved in a campaign. And the artwork is among the best ever. The only downside is the pretty steep price, but the book is well worth the money. If you only buy one supplemental, make it this one.