You might think that women would be tired of the Apha Hero. He's demanding. He doesn't explain himself or any of his actions. He's overprotective and hardly cares to hear if you've got a better idea....
The perfect example--Han Solo. Now I say this because heroes have become a little more complex over the last twenty years. Alphas showing signs of Beta, Betas showing signs of Tortured. Somehow, because of this I've spent the last twenty minutes wracking my brain for a good example. Han is a loner.
According to Modernman.com, an alpha male, upon entering a room, will assume high status, take on the role of the leader (or at least one of the leaders) and simply expect others to follow him and show him respect. Oh hey! I think I married one of these!!! :D Although, like a good leader, mine will look for the one who is ACTUALLY in charge instead of being an ass. One of the aspects that separates my hubby from being a beta is that he'll leave if he doesn't like what the other leader is demanding. A beta would NOT do this. :D
Look to your books for the best examples of a true Alpha Male. Elizabeth Lowell and Christina Dodd write alpha males that any romance reader can appreciate. Read about Archer Donovan in Lowell's Pearl Cove or Jasha Wilde(yes, we heard about him yesterday at Penny's blog, too) in Dodd's Scent of Darkness. You won't be sorry.