To get past all the BS on Ayn Rand, I'd recommend the new SEP article here. I'm not defending her (I'm nowhere close to an Objectivist), but it's well worth a read. Many people focus on her egoism and ignore the fact that she was a certain kind of virtue ethicist.
@ Due,
If you're sincerely interested, as I mentioned before, I'd recommend Eric Mack's recent book. It's cheap and it's probably the best introduction / overview of classical liberal / libertarian philosophy I've ever read. Here it is.
Mack usefully breaks up the ethical positions for libertarianism (and classical liberalism, hereafter just libertarianism) into three categories: (a) natural rights (think Locke, Nozick); (b) cooperation to mutual advantage (think Hume, Hayek); and (c) some sort of indirect consequentialism, e.g. rule or institutionalist (think the early JS Mill and many other political economists). Naturally, how those roads lead to libertarianism, and how they deal with the usual objections, vary.
If you have any specific questions, feel free to ask.