Giant enemies
If you repeatedly kill some types of enemy within a short period a giant version will appear. This applies most to the Stalchildren running rampant during the night on Hyrule field and the Guay located at Lon Lon Ranch.
Never lose tunics and shields
When a Like-Like is eating you swap to the Kokiri Tunic and Mirror Shield. Because neither can be purchased nothing in the environment is able to destroy them, and so the Like-Like can't eat them.
Free money
As young Link, travel to the gate in front of the city. Stand on either chain, and wait until night. The gate will be raised. Walk across the narrow end of the upturned gate to collect 80 rupees (four red ones). This trick can also be done during the day time, simply walk straight up the chain until your face is in the wall then turn towards the middle and jump down. You'll get 20 rupees while you're falling and enter Hyrule Castle Town.
500 Rupees
This trick requires Adult Link, the Biggoron's Sword, and (preferably, although not required) the Giant's Wallet. Enter the Lost Woods and turn left. There should be a Skull Kid standing on top of a tree stump. Approach him, and when he advances on you, quickly attack him with the Biggoron's Sword, using the stabbing-motion (forward+B). If you are able to defeat him before he disappears, you'll be rewarded with a special rupee, so big that it will fill any wallet you have, even the Giant's!
A similar reward can be achieved with the help of the Bunny Hood, which Young Link can obtain from the Happy Mask Shop once he has already sold the Keaton Mask, Skull Mask, and Spooky Mask. Once you've got the Bunny Hood, go to Hyrule Field, approaching Lon Lon Ranch. You should eventually see a man running laps around the ranch. If you wear the Bunny Hood and speak to him, he will ask you to sell it to him. Say yes and he'll pay you five hundred Rupees. (it is preferable that you have the Giant's Wallet for this)
Unlimited Rupees
Once you get all 100 Gold Skulltula coins, simply return to the last family member to receive a gold rupee. You can just leave the house and go back in and get another.
Gossip Stones
Attacking the Gossip Stones in various manners has no useful purpose outside of entertainment value; however, doing so can yield rather amusing results. Bombing a Gossip Stone will cause it to flash blue and red and take off after a few seconds. Hitting one with your Megaton Hammer will flatten it temporarily. Even comparatively boring attacks, such as with a sword or a hookshot, cause the stone to vibrate differently, depending on the weapon used.
Chicken Attack
Note: this is a rather dangerous (though quite amusing) pursuit, so do not attempt it if your health is low - one hit from a chicken depletes an entire heart container. If you are inclined to be attacked by an enormous horde of chickens, attack one repeatedly until it calls up its buddies, and then run as rapidly as possible in the opposite direction. Two of the better places to do this are at the entrance to Kakariko Village, where there is an easy escape route, or in Lon Lon Ranch, where you can attack them while riding Epona and be invincible to their attacks.
Sign Reconstruction
If you ever feel the need to take out your aggression on one of the larger wooden signs with a sword or bomb and subsequently realize that you actually wanted to read it, either leave the room or play Zelda's Lullaby and watch the sign put itself back together.