Display certain taxonomy terms in Select List? I have my content type set up something like this:

type (select):
  type1
  type2

taxonomy_term_reference (select):
  term1
  term2
  term3
  term4
  term5
  term6


When a user fills out my node and chooses type: type1, I want only these terms to show up as options:

  term1
  term4
  term5


When a user fills out a my node and chooses type: type2, I want only these therms to show up as options:

  term2
  term3
  term6


Is there any good way of doing this?  The only way I can think of is with custom code via hook_form_alter()?
Try reference-option-limit module. It has the ability to limit your reference field value.

Another approach is to use entity reference instead of term reference and add an entity reference display to a views and select what items you'd like.
Then in your content type reference field setting and under entity selection select the views you just created.

I hope this will help.