Is there a Biblical ban on gambling? Most churches and many Christians I know are strongly against gambling, but I can't recall any passage in the Bible that declares that we shouldn't gamble. Does such a passage exist?  

To clarify I'm not asking about whether it's wise to gamble, but whether it's a sin to gamble according to the Bible.
The Bible does not mention the word Gamble or Gambling. It does however, have a lot to say about money and the love of money. While I'm not a fan of posting a link and saying, "Hey, just go read this", the article below is well written and I believe it does a much better job of answering this question than I can.

http://christianity.about.com/od/whatdoesthebiblesay/f/isgamblingasin.htm

Here is a small quote from the article:


  Does the Bible Mention Gambling?
  
  Although the words "gambling" and "gamble" do not appear in the Bible,
  we cannot assume that an activity is not a sin simply because it is
  not mentioned. Looking at pornography on the Internet and using
  illegal drugs are not mentioned either, but both violate God's laws.
  
  While casinos and lotteries promise thrills and excitement, obviously
  people gamble to try to win money. Scripture gives very specific
  instructions about what our attitude should be toward money:
  
  Whoever loves money never has money enough; whoever loves wealth is
  never satisfied with his income. This too is meaningless.
  (Ecclesiastes 5:10, NIV)
  
  "No servant can serve two masters. [Jesus said.] Either he will hate
  the one and love the other, or he will be devoted to the one and
  despise the other. You cannot serve both God and money." (Luke 16:13,
  NIV)
  
  For the love of money is a root of all kinds of evil. Some people,
  eager for money, have wandered from the faith and pierced themselves
  with many griefs. (1 Timothy 6:10, NIV)
  
  Gambling is a way to bypass work, but the Bible counsels us to
  persevere and work hard:
  
  Lazy hands make a man poor, but diligent hands bring wealth. (Proverbs
  10:4, NIV)


*EDIT

About casting lots

The Bible does mention "Casting Lots" but I wouldn't define this as gambling. Proverbs 16:33 says: The lot is cast into the lap, but its every decision is from the Lord. Also, in Acts, the disciples prayed and then cast lots: And they prayed and said, "You, O Lord, who know the hearts of all, show which of these two You have chosen to take part in this ministry and apostleship from which Judas by transgression fell, that he might go to his own place." And they cast their lots, and the lot fell on Matthias. And he was numbered with the eleven apostles. (Acts 1:24-26).

I've always understood that when lots were cast among believers, it was as if they were asking God a question. I believe that it's important to note that lots were cast by the disciples before Pentecost. After Pentecost, casting lots was not mentioned again.

Once you have the Spirit, who needs to cast lots?

But when he, the Spirit of truth, comes, he will guide you into all truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. John 16:13