Small Niche Games is known for fantastic old school adventures. Inn of Lost Heroes, Pyramid of the Dragon, and Shrine of St. Aleena are some of my personal favorites. Tower of the Boon Companions continues SNG's trend of taking classic fantasy gaming tropes and turning them on their ear. Nominally set in SNG's world of Amherth, Tower of Boon Companions is still very much a "drop in and play" module. In addition to providing a unique adventure to keep your players on their toes, it also gives a small bestiary of new monsters for your Swords and Wizardry WhiteBox campaign, a handful of new magic items and the thief class - the latter of which was originally found in the White Box Omnibus by Barrel Rider Games.
For three bucks, you get several nights of great adventure, a corral of new monsters, a new class, and brand new magic items (one of which could kick off an entire campaign). Well worth the price of admission.