Not surprisingly, this is a Warren Buffett stock.A diversified portfolio with stocks in different categories and industries is the best way for most people to maximize their investments. If you have $1,000 available to invest and are in the market for an excellent dividend stock, consider Ally Financial (ALLY 1.15%). Here's why it could be the ultimate dividend stock.What makes a great dividend stock?The yield is probably the first thing on an investor's list when thinking about a great dividend stock. The ...