TooManyItems

TooManyItems is a mod created by Marglyph. The mod allows the player to visually choose and get directly in his inventory any object (blocks or items) from the game without the need to type any command like "/give " (unlike INVedit, which requires going to the menu to edit your inventory), including acquiring infinite stacks of items, blocks and infinite tools. As well as this, it also allows you to save up to seven different inventories and even throw stacks into the trash when they are not needed. The mod is currently compatible with Beta 1.9 pre. The mod needs Mods/Modloader to make unlimited stacks of blocks refresh automatically.

Trivia

 * In SSP, if you shift click on armour items, as an attempt to get infinite armour, and then equip it you will receive absolutely no damage from anything (with the exception of the void) even after the armour if removed or thrown away in the trash.

Download
The file can be downloaded here and has compatible versions for Beta 1.2 through Beta 1.9 pre5.