Let's give credit where credit is due.  The Van Richten books are an excellent set of sourcebooks for Ravenloft, and need to come back into printing.  But lets be honest, more players own those damn books than DM's.  I think players should read them, but too many people feel that those books are the end all, be all of Ravenloft.

  VAMPIRES
  Vampires are a Ravenloft staple.  Kind of like asphalt in the city.  Ravenloft needs vampires.  A hint of romance, a dash of terror, and a fearsome undead hunger that we can never understand.  More than one DM seem to run these creatures as replicants, or perhaps the borg.  They hardly ever have different feeding habits or methods, and Van Richten mainly stuck with the normal types of feeding, mouth to neck and mouth to arm or whatever.  After some crappy '80's movies, I came up with a few alternate ways of feeding.
  Mouths on fingertips or on the palms.
  Open the mouth and suck out the soul.
  A fanged maw on the end of the tongue.
  In combat, I make vampires immune to blunt or piercing weapons.  They may be super strong, or weak and flabby, depending on what I am running.
  MUMMIES
  Mummies exist in Ravenloft in more than Har'Akir, but are often overlooked unless the adventurers enter Har'Akir or another desert land.  Mummies have been created in places like Peru and Viet Nam, so weather is not the only dependancy.   Imagine the parties chagrin when they run into a mummy who is tough and leathery, hunting them in the jungles of Richemlot, an anchient jungle tribes shaman.  Mummies might also be immune to piercing and blunt weapons, and a tough, leathery mummy from a peat bog would be vulnerable to flames, and might have to be hacked apart like a cord of wood.
  WERE-CREATURES
  Lycanthropes are all over the place in Ravenloft, from were-anteaters to were-zebras, lycanthropes make excellent foes for the party.  Some have perfected the art of mingling with the population of a large town or city and stalking thier victims.  Some relish the thrill of hunt, others just get it over with,
  LOWER PLANES CREATURES
  Powerful.  Implacable.  Inhuman.  Monsterous.  Did I mention Powerful?  These beings think like no other creature you can ever face.  Most other foes in Ravenloft at least had human thought process at one time or another, but these have no human thought process at all.
  LICHES
  The undead husks of powerful wizards, these creatures are often overlooked by more than one DM, writing off the power and capability of a lich as far too powerful for their PC's to handle.  Liches can be used in many contexts, and they do not necessarily have to be massive power houses.  What is wrong with a 9th level of spell casting lich who happens to have several innate abilities uncommon to liches?  What about a troglodyte shaman lich, who is spell level W: 7 P:5, that is a powerful smount of spells, combined with underground abilites and fierce attittudes.  While not overpowering, it would definately be a major foe for a 5th level adventuring group.  Combine that with his undead trogs, in a series of haunted caves and you've got a quick and fun adventure.
  NON-CORPREAL UNDEAD
  Ahhh!  A ghost, a wraith, a specter, another bodiless spirit!  Attacks that Van Richten missed might be:  Leaning out of a tree, boulder or wall and swiping at a PC, tracking the party for their masters by hiding in a mount or piece of equipment.