Ok, this is about as easy as it gets, and is very popular with those who like this type of dressing.  Also I would note it contains no dairy, so it is fairly friendly for those with certain dietary restrictions.

Ingredients

• 4 parts mayonnaise
• 2 parts whole grain mustard
• 2 parts honey
• 1 part apple cider vinegar
• pinch of salt

Combine all the above ingredients, mix well, and refrigerate.  <Done!>
In a pinch, you can replace apple cider vinegar with most other types of vinegar (do NOT use balsamic).  You can also adjust the honey quantity to taste, but the 4:2:2:1 ratio is pretty good for most palates.
-Mike Rothman