Much-maligned Citigroup ( NYSE:C ) stock has rallied more than 40% off of its 52-week low. However, even after this rally, there's still plenty of room for additional upside. I'm bullish on shares of the fourth-largest bank in the United States based on its incredibly cheap valuation, above-average dividend yield, and the steady progress the company is making on reducing expenses. Furthermore, several highly-regarded value investors have positions in the stock and seem to support management and its turnaround plans.