What do Southern Baptists believe about Predestination? It seems that some doctrines and beliefs are not taught openly.  I was curious, what is the Southern Baptist doctrine regarding predestination?

Do they believe in unconditional election or complete lack of free will?
Historically, Baptists drew from both the Calvinist (Predestination) and Arminian (Free Will) soteriologies.  Early Baptists were first and foremost dissenters - people who disliked the establishment churches of England and Virginia.  

What drew them together was not soteriology but rather a disdain for establishment church.

The Puritans in particular (one set of proto-Baptists) were basically Calvinist. Many of the more famous English baptists - John Bunyan (1600s), William Carey (early 1800s), Charles Spurgeon (late 1800s), were all Particular Baptists. Many of their kin settled in Virginia and Massachusetts (or like Roger Williams in 1636 were kicked out and stuck in Rhode Island), and helped to form the basis of Baptists in the United States.

When the Baptist movement spread during the two Great Awakenings of the 1700s, much of it was fueled by charismatic Arminians, such as the Wesley brothers. In the 1700s in particular, Baptists and Methodists both were very closely related - the primary distinction between the two was the autonomy of the local congregation. Methodists had bishops, Baptists had "associations."  

By the time Baptists were allowed to practice freely (1786 is a good year) both stances were evident.

Eventually, there were two main camps of Baptists - "General" Baptists who believed in General atonement, i.e. anyone who chose (i.e. free will) to believe in Christ.  In contrast, "Particular" Baptists were Calvinists, who believed in Limited Atonement.  These are the Baptists who wrote the 1689 Baptist Confession of Faith, one of the closest things to a "founding Baptist creed" you'll get from a Baptist.  As you would expect from a Calvinist, they believed in predestination - i.e. that God has foreknown whom he would save from before the beginning of time.

When the Southern Baptist Convention was formed in 1845, the issues that divided Baptists had far more to do with whether or not Sunday schools and missionary work were important, than the means of salvation.  (Actually, the argument against was predicated on the belief that if God had already chosen who was saved, then it was just a waste of resources to invest in those things.  That didn't stop a a guy like William Carey, though, because he realized that even the elect should work to help the elect who didn't know they were saved to be saved!)

More to the point for Southerners was whether or not missionaries could own slaves.  The SBC has acknowledged this was their genesis, and apologized for it in the 1990s.

Throughout all of this, both strains of salvation continued through all the denominations, although many of the more prominent current Baptists (Paige Patterson, Al Mohler) are definately of the Calvinst persuasion. 

That said, the 2000 Baptist Faith and Message is clearly ambivelent on the matter.

Section 4. Salvation says:


  Salvation involves the redemption of the whole man, and is offered freely to all who accept Jesus Christ as Lord and Saviour, who by His own blood obtained eternal redemption for the believer. In its broadest sense salvation includes regeneration, justification, sanctification, and glorification. There is no salvation apart from personal faith in Jesus Christ as Lord.


implying free will

Section 5. Grace says:


  Election is the gracious purpose of God, according to which He regenerates, justifies, sanctifies, and glorifies sinners. It is consistent with the free agency of man, and comprehends all the means in connection with the end. It is the glorious display of God's sovereign goodness, and is infinitely wise, holy, and unchangeable. It excludes boasting and promotes humility. All true believers endure to the end.


which could come out of the Tu-lips of Calvin himself.

Incidently, there is a Free Will Baptists denomination who are most definately Arminian in their soteriology.

tl;dr
In short, Baptists have always been both.