May I recommend The Hamlet of Thumble? It has been described as one of the most value-packed items out there and is already ranked one of the Top 20 d20 products of all time, according to EN World.
THoT includes:
A short adventure
A fully-detailed hamlet with 58 NPC stats
3 New Core Classes: Cavalier, Shaman, and Witch
1 New Skill
7 New Feats
56 New Spells
12 New Magic Items
2 New Monsters
Mundane Weapons (kitchen knives, broomsticks, frying pans, etc)
A simple set of rules for morale Checks
An interesting article on "Incorporating Dreams Into Your Game"
Rules for Reputation Points
Special Abilities and Weaknesses for PCs
Starting a New Game
Distributing Ability Scores by Power Level
How to Avoid Killing 1st Level PCs
How to Keep Role-Playing from Becoming “Roll-Playing”
12 Signs of a Good DM
6 Good-Aligned Ready-to-Use Pre-Generated Characters
6 Evil-Aligned Ready-to-Use Pre-Generated Characters
Gary Gygax has described it as "innovative" and says, "The material is clearly written by a gamer for the enjoyment of gamers. Hooray!"
GamingReport staff reviewer Serge W. Desir says, "The Hamlet of Thumble offers an innovative approach that captures the classic atmosphere and fun of first edition D&D modules. The breadth of the environment, the great descriptions, and the attention to detail make this a truly enjoyable adventure."
There are more review quotes here:
http://www.openworldpress.com
I'd also recommend A Magical Medieval Society, Bluffside, Midnight, Tome of Horrors, and other products people have mentioned here.