Being the only metal which is liquid at room temperature mercury has some specialist uses:

It is used in thermometers because it has a large thermal expansion which is constant over a large temperature range although it is being phased out in favour of safer liquids. mercury/mercury3.htm

It is also used in barometers an manometers due to its high density. From this it has also become a way of measuring pressure in millimetres of mercury.

It has also been used as liquid electrolyte for the production of chlorine and sodium hydroxide from the electrolysis of brine but is again being phased out in favour of safer alternatives.

It is still sometimes used in electrical switches as a liquid contact.

Mercury also used to be used as a component for dental amalgams for making fillings for teeth. This process has again been phase out due to health concerns but many people still have mercury containing fillings and crematoria are thought to emit about 5kg of mercury each year simply from dental fillings. The amalgam of 70% silver and 30% tin when mixed with mercury formed a pliable material that could be inserted into the tooth and the amalgam expanded as it dried to fill the entire cavity. However this amalgam has been replaced by a similar one made from 60% silver, 27% tin and 13% copper. fillings.htm