Here is a prime example of how language is changing. Traditionally, whenever the verb in the sentence was a variation of the word “to be,” the pronoun following always had to be in the subjective case (I, you, he, she, we, or they) whether you were speaking or writing.
It is me.
It was them.
It is I.
It was they.
However, the correct way does sound overly formal in a normal conversation. Therefore, when speaking you can get away with this error.
Correct (only when speaking)
Last month the people with the most sales were you and me.
On the other hand, when writing, the grammar books recommend you stick with the rule.
Correct (when writing)
Last month, the people with the most sales were you and I.
Some variations of the verb to be are am, is, are, was, and were.
Isn’t grammar fun?