Change bowling ball colors
When starting a game of Bowling on Wii Sports, you will come to a warning screen. At this warning screen, press one of these buttons on the D-pad for the corosponding color:
Right = Gold
Left = Red
Up = Blue (Default)
Down = Green
Now, while still holding the button on the D-pad, click the "A" button to start the game. You will now be able to play with the color of ball you chose. Now, I don't know if it's just me, but it seems that the gold bowling ball gets more strikes.
Change tennis court colors
When you start a Tennis game, you will pick your Mii, and be faced with a warning screen. At this warning screen, hold the "2" button and press "A". You will switch from the green court to a blue court.
No maps and meters on Golf
Start a game of golf, hold "2" and press the "A" button on the difficulty you want to play. You will start the game without any maps or meters to assist you.