"Last but not least" is generally considered a formal expression. It is a common transitional phrase used to introduce the final point.
1. I would like to thank all of our sponsors, but last but not least, I want to thank all of the volunteers who helped make this event a success.
2. We have many reasons to be grateful for our parents, but last but not least, we appreciate their unwavering support and encouragement throughout our lives.
2. We have many reasons to be grateful for our parents, but last but not least, we appreciate their unwavering support and encouragement throughout our lives.