Descriptive, Prescriptive, Semiotics, & Variation...Oh my!

Was asked this question online once. Thought I'd pose it here and get your input: There [is / are] a vase and a flower on the table.

Click on the link above to see the thread that led to my response below...

Ok, so  we are talking about (a) descriptive English (i.e., how English is actually used), prescriptive English (i.e., what the book(s) say), (c) idiomatic expressions, and (d) English variation.  Anita alludes to a syntactic (and semantic/pragmatic) alternative as well.  I've always been of the belief that it's better to discuss each of the above issues with students instead of having personal opinions sway me in any one particular direction.  As far as (traditional) testing is concerned, I've stuck with prescriptive English over descriptive for the most part but this has not refrained me from teaching students other varieties of English (American/British English, descriptive/prescriptive, etc.).

Personal opinions aside, how would you go about teaching these different expressions?  Or do your personal opinions lean you to one particular style of English being taught in your classroom?