Pokemon - http://phatbowling.com/zapdos45/Fake_Red_and_Blue

Bill's Garden

You must have all 150 pokemon for this cheat.
Put the following pokemon in your team in this order(from the top): Articuno, Zapdos, Moltres, Dratini, Dragonair, and Dragonite. Go to Bill's house (Sea Cottage) and talk to Bill. He will let you in to his garden where you can find Togepi and Marril!

Fish for Items

Talk to the man that gives you a super rod 100 times and he will give you an ultra rod.
You can fish for items like HM06 (hi-fly) which you teach to a pokemon and fly to new myterious cities. You can also fish for HM07 (deep dive) which you use to go under the water and find new pokemon such as Houhou and Lugia. I heard you can also get a mist stone that evolves Gengar into Spooky.

Get to Cloud City the Easy Way (Yellow Version)

Beat the Elite Four. When it is the Hall of Fame (when you and your pokemon are shown) While your pokemon are showing in the Hall of Fame, quickly press: B, A, UP, DOWN, LEFT RIGHT. When you are standing in front of your house go to your computer, it will say there is a glitch in the game. Then go to your T.V. and press it and it will tell you what's on it. Then go to your bookcase, it wil say 'crammed full of pokemon books' then go to Proff Oak's lab and press one of the poke-balls on his table, even if you don't get it. Then go back to your computer in your house, it will ask you 'do you want to go to cloud city?' press yes and you will be sucked into your computer and taken to cloud city!

It is rumoured that there are all 151 pokemon in Cloud City, and HM06: Beamer which is used to beam back to Cloud City whenever you want!