Extraterrestrial liquid water
The Gliese 581 planetary system contains multiple planets that may be candidates for surface water, including Gliese 581c, Gliese 581d, might be warm enough for oceans if a greenhouse effect was operating, and Gliese 581e.
Metallic hydrogen
At high pressure and temperatures, metallic hydrogen can exist as a liquid rather than a solid, and researchers think it might be present in large quantities in the hot and gravitationally compressed interiors of Jupiter, Saturn, and in some exoplanets.