ANSWER: The Bible records at least seven people committing suicide. The first one mentioned performing this desperate act is Abimelech, one of Israel's Judges. He took his own life after he was severely wounded when a huge millstone landed on his head (Judges 9:52 - 54). Samson famously committed suicide in order to bring destruction on the Philistines who had, for years, harrassed Israel (Judges 16:30).
King Saul and his armor bearer committed suicide after Israel lost a battle to the Philistines (1Samuel 31:4 - 5). King Zimri, ruler over Israel for only seven days, killed himself when the people rebelled against him. He committed suicide by burning down to the ground the palace he lived in (1Kings 16:8 - 18).
Ahithophel was a trusted confidant of Absalom (King David's son). He ended his life by hanging himself when his counsel was rejected (2Samuel 17:23). Judas Iscariot, the only recorded suicide in the New Testament, "hanged himself" (a likely reference to stabbing himself with a knife) after betraying Christ.
The greatest overlooked suicide in Scripture, however, occurred with Lucifer and one third of all the righteous angels. They killed themselves spiritually when they decided to rebel against God and willed themselves to forever be his enemy.
The act of killing oneself is a very sorrowful event. It is especially hurtful to those who know the person and even much more the family. BibleStudy.org offers its condolences to anyone grieving over the loss of someone due to taking their own life.
The world looks upon suicide in a twisted manner. People tend to categorize sin but the Bible does not! James said if you keep all of God's Law and break one little point you are guilty of breaking all of it (James 2:10). According to Jesus Christ himself, if you just have a thought in your mind with hatred toward your brother you are guilty of murder (Matthew 5:21 - 22). Hating yourself, therefore, is murder, and a breaking of the sixth commandment (Exodus 20:13).
Suicide is murder of oneself and is a sin, but it is not the unpardonable (unforgivable) sin. The Apostle Paul, in the book of Romans, states that because we all sin we all have a death penalty upon us (Romans 3:22 - 23). All humanity stands guilty before the Eternal.
The taking on one's life via suicide is, sadly, an all too common occurrence amongst humans (1Corinthians 10:13). It does not make a person the worst sinner in the world. God promises that if we confess our sins he is more than willing to forgive us and cleanse us of all unrighteousness.
The Bible states that the ultimate hope for anyone who felt it necessary to commit suicide is the second resurrection of the dead. This is a time when God will bring back to life all those who never fully understood his truth and therefore never repented of their sins. It is a time when countless billions will have their minds opened and given the opportunity to receive eternal salvation.