Assalamu`alaykum,
Bismillah.
Bismillah.
Narrated Aisha:
Whenever Allah's Apostle saw the rain, he used to say, "O Allah! Let it be a strong fruitful rain."
For those who are new to this du`a, this is how you say it:
Allahumma sayyiban naafi`an
Plus, when it rains, make all the du`a that you want. Because it's one of those special times when Allah accepts the du`as of His slaves. :)
Wassalam.