Bukkit

Example config.yml (In this config, people with the perm CustomDrops.vip would get a chance of getting Gold/Iron Blocks from Gold/Iron Ore and Golden Apples from grass):

IRON_ORE:
  NORMAL: $IRON_INGOT,1;IRON_BLOCK,1,5!vip;
  SILK_TOUCH: IRON_ORE,1
GOLD_ORE:
  NORMAL: $GOLD_INGOT,1;GOLD_BLOCK,1,5!vip;
  SILK_TOUCH: GOLD_ORE,1
GLOWSTONE:
  NORMAL: GLOWSTONE,1
  SILK_TOUCH: GLOWSTONE_DUST,2~4
GLASS:
  NORMAL: GLASS,1
BOOKSHELF:
  NORMAL: BOOKSHELF,1
GRASS:
  NORMAL: DIRT,1;$GOLDEN_APPLE,1~3,5!vip;

Okay, now let's break down the config.

BLOCK_NAME:
NORMAL: DROP_INFO_GOES_HERE;NEXT_DROP_INFO_GOES_HERE
SILK_TOUCH: DROP_INFO_GOES_HERE;NEXT_DROP_INFO_GOES_HERE

BLOCK_NAME:
Can be any block... Click here to see a list of bukkit materials.

NORMAL/SILK_TOUCH:
Either NORMAL or SILK_TOUCH (SILK_TOUCH will only occur if pickaxe has Silk Touch enchantment, normal will occur without Silk Touch, or if SILK_TOUCH is empty).

DROP_INFO:
FORMAT: DROP_NAME,DROP_AMOUNT,DROP_CHANCE
DROP_NAME: Any item that can be dropped. Click here to see a list of bukkit materials.
DROP_AMOUNT: Minimum amount and Maximum amount seperated by a ~ (Example: 25 to drop 2 to 5 drops)
DROP_CHANCE: Leaving this empty will result in 100% chance of drop. Chance out of 100 to drop this drop. (For 50% chance leave "50", etc.)
OTHER: Add a $ in front of DROP_NAME to allow fortune picks to give extra drops (I don't suggest you put a $ if the drop is the same as the block). Add !test after DROP_CHANCE to set a permission for that certain drop (For !test the perm would be CustomDrops.test).