Jordan Cross was able to see people's last moments before their deaths when he touched them.
Ezra Small was the founder of Smallville, and known for his prophetic visions which he wrote down in code.
Clark Kentwas able to predict the 2005 meteor shower in a dream. He also in a separate instance saw himself as Superman in a dream well before he donned the cape.
Kent Nelsonwas able see the fate of others except his own using the Helmet of Nabu.
Two out of the three precognitives are known to have gained their powers from kryptonite exposure. Both of these precogs need to touch people in order to see the future.
No precognitive has ever become psychotic as a result of their kryptonite infection.
It is unknown how Ezra Small gained his ability to see the future.
Precognitives have only been used for evil once by a villain; in the online comic Smallville: Visions, Lex Luthor attempted to prevent his eventual death by forcing Jordan Cross to see his future.
Lex Luthor's future is so horrifying that it has caused death or unconsciousness in both precognitives that he's touched: Jordan Cross and Cassandra Carver.
Both Jordan and Cassandra were comforted by seeing Clark Kent's future.
According to Jordan, Clark Kent was one of the only people who could change a future once Jordan had seen it.
Jor-El (as an artificial entity) was able to show Clark Kent what his future would have been like, if his ship had not made it to Earth. While not technically precognition, it displays an ability to manipulate time and the future that goes well beyond precognition.