Increase Units

At the game mode screen, highlight "All Right?", hold Select, Start & Down and press B. Now, when you buy units, they will be worth 20 instead of 1.

Infinite Warps

After using a warp, instead of choosing "next", choose "End" and when the "Side Change" message comes up, press B to say no. Now you'll be able to use the warp again.

See The Ending

During the intro, hold A + B + Select + Top-Right and press Start to watch the Alliance ending. However, also during the intro, if you wait for the huge red ship to appear and do the same code, you'll see the Bacterion ending instead.