Mods in Minecraft have introduced many new liquids beyond vanilla Minecraft's water, milk, and lava.
BuildCraft
Forestry
- Liquid Honey
- Seed Oil
- Biomass
- Ethanol (Formerly Biofuel)
- Short Mead
- Apple Juice
Railcraft
- Creosote Oil
- Steam - Not a liquid in a complete sense since it can't be picked up with buckets, but it can be stored in tanks and pumped in Waterproof Pipes or Liquiducts.
Thermal Expansion
- Molten Redstone
- Molten Ender
- Energized Glowstone