There are several questions that you must ask regarding objectivity of resources.
First of all, is the information presented without bias for or against the subject or are there subjective statements or opinions?
What choice of words are used? Are they "loaded" terms (terms meant to sell something, or manipulate or persuade you) or are they terms which inform only?
Are there errors - either in logic or through missing facts or issues?
Is there advertising present (particularly in articles or on web sites) is it differentiated from the informational material provided?
Are there games, contests, giveaways, or celebrity endorsements present?
Objectivity is clearly related to the previous three criteria - authority, purpose and accuracy. Think again about the Holocaust deniers - their objectivity is often not present because they so vehemently espouse their views in spite of historical evidence to the contrary. Objectivity, or lack thereof, may not be as obvious on other topics so keep in mind the above questions when looking at the sources.