Secrets (Harvest Moon: SNES)

Quick Cow
Once you give an adult cow a miracle potion, give it medicine RIGHT after that. This will make a baby cow be born in 3 days instead of 30.

Ending Preview
Once you go to sleep, hold down R, L, START, and SELECT while the screen is still dark. This will let you see which ending you are headed for.

Money Tree / Bell Tree
Have 20,000G when fall arrives and buy it from the Hawker.

Magic Bean
Sell a cow. If the Hawker comes and offers a bean for the cow, take him up on the offer and be prepared for a surprise!

Choose Baby Gender
As soon as you're wife has given birth, do NOT name it!! Leave and go to the village and talk to someone who SHOULD be at you're house but isn't. Then, return to you're house and you're wife should have given birth to the same child again. But this time it will be the opposite gender it was the last time! Note that you still only get 1 child by doing this.

A Rabbit for 1000G
At some point in the game, you can find a rabbit on the mountain. Run up to it, press the a button, and catch it. A hunter will show up and offer you the money if you let it go. I do not know if this event can happen more than once however. I've had it happen, but never saw the event a second time.