The Legend of Zelda: Twilight Princess

Cannon Room
If you've saved in the huge cannon room when you are first introduced to it and you quit, you will be stuck. That's it. Game Over. Start anew. I'm pretty sure if you save at all and continue playing it will still not let you progress. I urge you wait until you progress to a point that it wont be an issue.

Fishing with Ganon
The true final boss of this game, Ganondorf's last form, can be distraced by the fishing rod. Just cast it out while Z-Targeting him and his head will turn to look at the lure. Quickly put away the fishing pole and get in a few quick attacks. Remember to finish him off with a split-second strike when the oppurtunity arrises.

Control a Cucco!
Unlike other Zelda games (where you got attacked if you hit the Cuccos), in Twilight Princess if you hit a Cucco about 8 times, you'll be able to control it for a short period of time.

Infinite Bomb Glitch
First, as a wolf, play PLumm's minigame with the fruit and crash. Then, turn back into a human and turn to the water behind you. While swimming in it, equip the hookshot, and while it is held out, strafe to the side and through the wall. If it works, you'll be swimming through the wall. Keep swimming until you fall and die. Now, as you wake up, Plumm will come back and ask to to play again. Say yes. Then crash at the beginning again. You should wake back up in the beyond-the-wall area from before, but you can stand. Turn into a wolf and jump into the waterfall. Then, you'll wake up in front of Iza's assistant. Say yes, and you'll go to her cabin. The boat will take off without you, and you'll be a wolf. So now, warp anywhere you want, and you'll have infinite bombs.
Note: Sadly, This ends when you turn off the game.

Magnetic Ceiling Glitch
This can be done wherever there is a magnetic ceiling, such as the first one encountered in Death Mountain Mines.
First equip the boots to the D-pad but don’t put them on. Go under the magnetic field and equip the boots. In mid flight up to the ceiling press the - button and put an item where the iron boots were on the D-pad, and make sure the Iron boots are not anywhere on the D-Pad. Unpause the game and finish flying onto the ceiling. You should be on the ceiling with the Iron boots off and you will stay there and be able to walk faster.
To get down walk off the magnetic part of the ceiling or equip and unepuip the Iron Boots.

Donation Reduction
Donate 1000 rupees to Goron inside the Malo Mart in Kakariko Village (you must progress past the third dungeon beforehand). Talk to the old Goron outside the shop and complete the quest he offers. Once completed, the second donation amount will be reduced from 2000 to 200 rupees.

Easily discover Heart Pieces
To easily find the locations of all Heart Pieces, go to Fanadi's Palace in Hyrule Castle Town and pay her 10 Rupees for a Love fortune. You will then see an area in the game that will contain a Heart Piece around it, obtainable in some fashion. You can keep paying her to show you other locations, but she will sometimes repeat the same location a few times over.

Worms for Fishing
If you go into the fishing hole behind the sign at the very entrance there will 3 little mounds of dirt.
Turn into the wolf and dig these up, earth worms will appear, scoop them up in an empty bottle and use them as bait for your fishing hook to make fishing extra easy!