[This was another fun question from my Kenyan experience]:
Genesis 1:26 reads, "
Then God said, 'Let Us make man in Our image, according to Our likeness; and let them rule over the fish of the sea and over the birds of the sky and over the cattle and over all the earth, and over every creeping thing that creeps on the earth.'"
If "us" does not imply the Trinity, then who is "us?" Our options are simply: 1) The Trinity; 2) God, speaking to Himself in "plural of majesty;" that is, in the vernacular of the majestic. 3) God + whoever else may be present. 4) I can't think of another option.
Since option 4 speaks for itself, let's consider option 3. Why would God add or be added to whoever or whatever may be present? Regardless of the reason, why would He want to make something or someone else based on that conglomeration? There is no reason for any such action, as He is all goodness and everything excellent. If by "us" God intended to make man in the image of Him + something inferior to Him, what does that say about God? Since God cannot change or be changed, this option does not follow. Is God incomplete that He requires an addition?
"Jewish tradition generally maintains that the plural is to be explained as God taking counsel together with the angelic assembly in the work of creation. Against this is the clear scriptural affirmation that only God creates and that the angesl, as created beings, cannot be creators with Him." (Merrill, Eugene. "Is the Doctrine of the Trinity Implied In the Genesis Creation Account?"
The Genesis Debate.)
Option 2 is plausible, but incomplete. "Plural of Majesty" may also be thought of a "The Royal 'We.'" For example the Queen may say, "we are not amused." This is a ruler who speaks with a collective voice, the voice of the people. The problem with this view is that "plural of majesty" is not an ancient form--it is relatively new. Mark Twain has helped to realize that people with tapeworms and pregnant women may also use this term, "we shall have our bath now." What if what the Queen says is NOT representative of the people? Interestingly, the Qur'an is "we" and "us" statements. Can the Christian point to these passages and say "there is proof of the Trinity" based on this premise? Islam will quickly defend itself by saying that this not the case at all, but merely one person speaking with a collective voice. This really supports the Muslim position and the Christian foothold becomes shaky.
We should not be so quick to give up our stance, though. While there is still only one person speaking, "plural of majesty" still may be useful because we are learning something about God we did not know before. He is not merely a passive creator, but one that is simultaneously majestic, transcendent, powerful, holy, mysterious and exceeds the limitations of grammar, "including the singular noun form" (Merrill).
The only solid option is the first, but here's the catch: we only know this teaches the Trinity in retrospect. If you lived in Moses' time, you would not have heard or read this and thought, "He's talking about one God who exists in three persons!" From the aspect of the progress of redemption, we are getting prepared for the idea (the seed is planted) but not fully understood until much later (when it comes to fruition). The doctrine of the Trinity is not the point of the passage, but there is the heavy hint especially considering who was moving over the surface of the waters. That was not an impersonal force agitating the waters, but a person described as a Spirit who will later say He wants man made in His image.
