Loleditor.

Loleditor is a more advanced Inventory editor, updated for the latest version of Minecraft.
Features:
Editing values like HP, Dimension, Fire, etc.
Changing spawn (and player) position
Editing inventory
Randomly-generated inventory (I don't know what's the purpose of it... only for lolz)
Saving inventories as packs for quick reloading

to change item properties (id, quantity, damage) click it with Right Mouse Button
to quickly change all items quantity to it's maximum (for example: dirt to 64, redstone dust to 64, but snowballs to 16 and diamond pickaxes to 1) press Full button
to quickly repair all items press Repair button
to delete only one item drag it to "Trash button" (clicking it (no dfragging) will clear all inventory)

How to use it:
1. Run LolEditor (seriously), open your world (button on left).
2. Edit whatever you want (to add item to your inventory you have to drag it from bottom of window to (surprise) your inventory).
3. Save world (second button).
4. Load world in (another surprise) Minecraft.
5. If you want to quickly edit your save once again:
5.1. Save it on Minecraft
5.2. Press reload button on LolEditor
5.3. Edit whatever you want
5.4. Save it
5.5. Load world in Minecraft