Battleship on Windfall Island
At the top plaza of Windfall Island in the building across from Mrs. Marie's school you can play a game similar to battleship. You'll be charged 10 rupees to play. You have 20 bombs to try and blow up 3 ships. There are 3 sizes of ships, one that takes up 2 squares, one that takes up 3 squares and one that takes up 4 squares. If you blow up all three ships you'll be rewarded with a piece of heart.
If you win a second time he'll reward you with a treasure chart. After that you'll win 50 rupees for winning.
If you beat the high score using less than 20 bombs you'll another treasure chart.
Letter Sorting on Dragon Roost Island
On the second floor of the Rito tribe village there is a post office where you can earn rupees sorting letters. Your goal is to match the seal on the envelope with the symbol on the shelf and throw the letter.
In the first round you have 30 seconds to sort 10 letters. You're rewarded with 1 rupee for every 2 letters.
In the second round you have 30 seconds to sort 20 letters. You're rewarded with 1 rupee per letter.
In the third round you have 30 seconds to sort 25 letters. This time if you get more than 25 letters you're rewarded with 3 rupees per letter.
The postman will ask you to come back and give the new guy some pointers. If you leave the area and come back the new guy will be there. He'll ask to see the legendary 25 letter sort. If you sort 25 letters in 30 seconds he'll ask you to put a letter in the postbox for him.
Some time later you get letters containing you rewards. A letter from the new guy has a Red Rupee and a letter from his mother has a Piece of Heart
Boating Course
Start this by talking to the NPC on the south island of the Boating Course islands. It costs 30 Rupees to start, then you follow the course collecting as many rupees as you can and finish before the time runs out. You get 4 minutes on your first try but the time decreases after that. Be sure to jump over the vertical barrel to avoid being knocked overboard; this is where high value gems are located. This game is for Rupees only — there are no heart pieces or charts as rewards.
Target shooting on Spectacle Island
Talk to the proprietor on the highest part of the island to start the game; it costs 50 Rupees per try. Note, you can only play during the day. There are 5 "pirate ships" (actually barrels) floating in the water and you get 10 shots to sink them all with a cannon. Use the analog stick to aim each shot and pay attention to where it lands so you make adjustments for the next try. The angle of the cannon can be from 15 to 50 degrees and the steeper the angle the farther away the shot will land. The first two prizes are a Piece of Heart, a Treasure Chart, and you get Orange Rupees after that.
Tips: Start with the closest barrel and work your way back, that way you'll already have a good approximation of the angle to use when you get to a new barrel. Change the angle in increments of 5 degrees, but use 10 degrees if you need a large change in distance.