JOEL - "But to us [there is but] one God, the Father, of whom [are] all things, and we in him; and one Lord Jesus Christ, by whom [are] all things, and we by him." (1 Cor.8:6)
As I explained this verse in my response to Pam, the verse says "to us there is but one God'. Or in other words, as far as we are concerned ("to us") there is but one God.
I know there are a few other scriptures in the Bible that seem to suggest that there is only one God. Period! There are even some in our own Book of Mormon that seem to imply the same.
They way I understand it, God dispenses eternal truths "line upon line, precept upon precept" (2 Nephi 28:30, Isaiah 28) as man is ready to receive it. While Jesus was on the earth His primary goal was to try and teach the simple truths about His Gospel to a simple people who had never heard it before. Because it was new to them, they may not have been ready to comprehend the idea that there are other Gods over other universes past, present, and future.

As Paul explained:
"I have fed you with milk, and not with meat: for hitherto ye were not able [to bear it], neither yet now are ye able." (1 Cor. 3:2)

Therefore, He kept to the simple concepts of love, faith, repentence, and keeping the basic commandments in order to give them something to start on. Why confuse them by explaining to them the existance of other gods when they are still trying to understand the basics? This also goes for the people in the Book of Mormon times.

God has told us, however:
"Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets." (Amos 3:7)

And that as we do keep His commandments that He will in turn impart to us more knowledge:

"For behold, thus saith the Lord God: I will give unto the children of men line upon line, precept upon precept, here a little and there a little; and blessed are those who hearken unto my precepts, and lend an ear unto my counsel, for they shall learn wisdom; for unto him that receiveth I will give more; and from them that shall say, We have enough, from them shall be taken away even that which they have." (2 Nephi 28:30)

And so, throughout the history of the Christ's restored Church, we have "hearkened unto His precepts". And because of that He has given us more understanding about the nature of God and other advanced concepts of eternal progression through our latter-day prophets. The Bible scriptures don't say much about these things, so latter-day revelation is just about the only way we have been able to learn about them. This of course is hard for anyone to accept who does not believe in latter-day revelation from God.