I too find nothing in Scripture that would forbid trading in stocks. If God has given us gifts and resources we serve Him best by putting those gifts and resources to good use. If we hoard (or hide) these gifts and/or resources then I believe we are not fulfilling His best for us. Some folks (like ZEEV!) obviously have a great talent for such endeavors. To not use these talents would be akin to an athlete or a musician or dancer never expressing their God given gifts.
When I used to compete in Track (Javelin) my personal motto was: His gift, my joy, His glory, our victory (or defeat! Lol!) In short, I felt I was honoring God by developing and using my God given "gifts" to the best of my ability. In my opinion someone who has the gift of buying and selling (anything legal) is no different. They have a God given gift - let them use it!