Anyone with vision, courage and the ability to inspire.
Balmer could always execute, but that's not what Microsoft needs right now. It doesn't know where it's going, so it's meaningless how well it gets there.
Microsoft, for better or worse, is still in the driver seat. In terms of market share, Apple is a rounding error. But they inspire. They are exciting people about the future. When was the last time Microsoft did that? This isn't just about share price; it's about perceptions by investors, customers, employees -- everyone. They need to inspire again.