Dwarfs

 Dwarfs (or Dwarves) are an easier fit than Elves.  They have been portrayed fairly consistently across editions and popular culture at large.  Sleepy, Bashful, Doc could fit right in along Gimli or Flint Fireforge.  Really the only trick is their sudden ability to use magic in modern D&D.

My baseline for D&D Dwarves

• Dwarves is a mis-translation of the their word for themselves which means roughly "Born of the Earth" and in their own tounge sounds closer to "Dwarfs".  It has since come to be used to describe any short person in the human tongues.  Dwarves do not care for this fact, and this may contribute to their reputation for grumpiness.
• While they can live for centuries, they age in a manner proportional to humans, lending most Dwarves an aged appearance for most of their lives.
• Dwarves are burly and wide compared to humans, their arms are broader and longer as well but their hands are deft.
  
• Dwarfs believe they were crafted by higher powers and trace the most ancient parts of their culture to mountain strongholds.
  
• Hair is not seen as unattractive on Dwarf women, many have facial and body hair of varying prominence.  Some Dwarf women have adopted the trends of their neighbors, leading to some confusion about the existence of Dwarf women and/or their beards.
• Dwarfs value toil, self sufficiency, and clan/family commitments.  This gives them a unique outlook on trade with outsiders.  This has led to misunderstandings which are the origins of their reputation for greed and in some cases wickedness. 
• Dwarfs have always used magic, but their traditions are steeped more in animism and they tended to distrust the more "sterile" magic practiced by humans.
  
• Most Dwarves tend to keep to themselves, be it in their mountain cities, local mining  settlements, or within a city trade district.
• Dwarf settlements, particular those in the mountains are are dizzying maze of mining tunnels, work spaces, and dwellings.  Grand halls and other specified areas are typically the vision or a particularly motivated leader or individual.  When you see a specific fortress, hall, or building made for outsiders, it is usually less a gesture of hospitality and more one of practicality, to keep outsiders from getting int he way.
• Dwarfs have learned to leverage the particular ecosystem of the world below to cultivate all manner of specialized flora and fauna, providing adequate agriculture.
  

This basically covers your traditional D&D/Tolkien dwarf, leaving room for the various sub-races and your more ancient Norse/Howardian malevolent being that bursts from the ground.