Over at io9, Rob Bricken has posted on thirteen of the strangest deities in Dungeons & Dragons. There’s a wide range of deities presented here, covering many different races and beliefs, and some callouts to some inconsistencies in some of the subject areas that each have domain over. While some may argue that these aren’t truly some of the strangest that have ever existed, they’re a good selection. A large list of many of the gods that have appeared in various editions of Dungeons & Dragons appears over on the Dungeons & Dragons Wiki Dieties page. There have been a number of other articles in the past looking at strange deities in D&D, including articles in Dragon 398’s Unearthed Arcana but you can also look to the real world for inspiration to find strange deities worshipped currently and in the past.
Of course, the recently released Petty Gods: Revised & Expanded Edition [AL] pretty much destroys this list and begs for at least a dozen more lists to be made.