Too Many Items is a Minecraft Mod that allows you create and delete items in-game, including mod items.
You can save and load entire inventories, create unlimited stacks and tools, test mods, create huge survival worlds, and much more. Too Many Items works in both singleplayer and multiplayer mode and you may find it even better than playing Minecraft in creative mode.
To install Too Many Items, just put the file in your mods folder. However, you'll also need to copy the classes into your minecraft.jar. There are several YouTube tutorials to help you if you have any problems.
Too Many Items includes unlimited stacks (which can be activated by shift-clicking) but you will need ModLoader for Minecraft for them to refresh constantly.
The full controls for Too Many Items can be found on the MinecraftForum.net forum.
Too Many Items is a powerful and comprehensive Inventory editor for Minecraft.