NOTE: Doing this during a saved game file will delete all the pokemon you ahve in your box!  I found that out the hard way.

Start a new game as either a boy or a girl

Save it right away!

Then start a new game as the opposite sex than you chose last time

And save it again right away

But when it says Saving, dont turn off the power, turn off the gameboy.

When you continue the game, your character will be the wrong color!
Normal Boy:
Wrong Colored Boy:
Normal Girl:
Wrong Colored Girl

 

Go to Vermillion.  Talk to the machop there.  Then go to Start->Pack->Key Items.  Then use the Coin Case.  The game will reset.  BTW, after you do this, dont turn the gameboy off.  Keep going to the title screen, and you can actually see Ho-oh/Lugia.

 

To see how to this, go to Prof. Glitch's Site

Here is what you do.

Continue your saved game and save again.

Start a new game, only this time be the opposite sex. (if you were a boy, then choose girl, if you were a girl, then choose boy.)

Now go to same place where you just saved, and save the game once again.

But when it says: Warning...Do Not Turn Off Game, shut the game off.

When you restart, continue the game again.  Now you will be the opposite sex, but still in the same saved game!!

 

This is easy.  When you battle Sabrina, look at her Mr. Mime.  Its a female!!!  The female sign next to its name indicates that its a female.

 

This is easy.  Use rock smash on a rock, stand where the rock was, and save the game.  Then the game back on, and...your standing on the rock!!!

 

Start a new game and get to Cherrygrove.  One your there, go to the PC in side the Pokemon Center, and turn it on.  your head will be above the border, at the bottom of the thing that pops up.  Also works on the upstairs PC.

 

Just go to your mom and keep on turn Daylight Savings Time on, and then off, and then on, and then off, ect. They WILL call!

 

Go to Entei and click on call, then quickly move up to Raikou, and the call will be distorted!

Thanks to sheer cold from serebiiforums.com