I think that you are probably going to be examining quotes that Gorbachev has said from the later portion of the 1980s. In the early stages of his leadership, I think that there was not as much of a strong voice towards the ending of the Cold War and the embrace of an approach that was so radically different than Soviet- style Communism. Consider a quote like this one from Gorbachev in 1987:
Our rockets can find Halley's comet, and fly to Venus with amazing accuracy, but side by side with these scientific and technical triumphs is an obvious lack of efficiency in using scientific achievements for economic needs, and many Soviet household appliances are of poor quality.
I think that this is a great quote because it was one of the first moments that a Russian leader was able to be honest about the state of Russian life under Soviet- style Communism. Here is a statement that is not propaganda or concealment of the truth. The fact that we now know, which at the time few did, was that Russian life was impoverished under the leadership of the Kremlin. Gorbachev's quote brings this to light before the official end of the Cold War.
Another bevy of quotes can be found in the speech to the UN General Assembly in December of 1988, where Gorbachev speaks to a vision of what can be. A radical departure from his predecessors, Gorbachev spoke openly as to what the future for the world in a post- Cold War world could be:
We are witnessing most profound social change. Whether in the East or the South, the West or the North, hundreds of millions of people, new nations and states, new public movements and ideologies have moved to the forefront of history.
There is much more in the speech that can be used as representatives of solid quotes from Gorbachev. Yet, my favorite is a quick one when asked in May of 1989 about what he thought on if the Berlin Wall should be torn down:
This is a great quote that really captures the essence of what made Gorbachev such an instrumental and powerful leader.