Joseph Smith used a verse in 1 Corinthians to justify his belief in many gods. Mormons have continued to cite this verse as Biblical support of polytheism.
"Paul says there are Gods many and Lords many. I want to set it forth in a plain and simple manner; but to us there is but one God that is pertaining to us; and he is in all and through all, but if Joseph Smith says there are Gods many and Lords many, they cry, 'Away with him! Crucify him! crucify him!'"
-Joseph Smith (Documentary History of the Church Vol 6: 23 Discourse of Prophet 474, 6)
Now, let's look at the actual verse that Joseph Smith is referencing.
"As concerning therefore the eating of those things that are offered in sacrifice unto idols, we know that an idol is nothing in the world, and that there is none other God but one. For though there be that are called gods, whether in heaven or in earth, (as there be gods many, and lords many,) 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 Corinthians 8:4-6)
It is easy to see that Joseph Smith took Paul's statements completely out of context. Paul clearly states that there is only one God in the first verse. He also clearly groups the gods many and lords many with those that are called gods, not giving them actual godhood status. Finally, since he states that there is only one God and then references both God, the Father, and our Lord Jesus Christ, he is also demonstrating support for the view of the Trinity.