In an effort to not make this longer than it has to be, I'll jump right in.
1) He is the only candidate who understands the nature of the "War on Terror" and is willing to tell uncomfortable truths about it. We aren't in the middle of an inevitable clash of civilizations, and we aren't being attacked because "they hate freedom."
In the 1980s, the CIA trained Usama bin Laden and the Mujahideen to drive the Soviet Union out of Afghanistan. Our CIA funded the group, gave them weapons, and capitalized on the Muslim fear of foreign occupation in order to push out the Soviets. We used UBL as a proxy to enforce our policy of containment of the USSR. America is now in the position of a man who trains an attack dog to go after his enemies, only to have that dog attack his kids.
When you're in that situation, the proper course of action is easy to see: you put the dog down and you stop training attack dogs. Yet, almost six years after 9/11, UBL is alive and well. Have we at least learned from our mistakes and stopped training attack dogs? Of course not! We're arming the Sunni insurgency in Iraq, so long as they promise only to fight Al Qaeda! Instead of dealing with both the problem and the policy that led to it, we're ignoring the real threat, and further destabilizing a historically volatile region using the same failed Wilsonian foreign policy that got us into this mess.
Ron Paul is the only candidate on either side of the aisle who is talking about actually changing our foreign policy at a fundamental level. While the "top-tier" candidates bicker over whether we have to "democratize the Middle East" as a unilateral action or with the help and assistance of the UN and our enemies in the area, Ron Paul has consistently been the lone voice of reason saying that we have no national security interest in the Middle East, other than leaving that god-forsaken desert.
2) He understands and will talk about the inner workings of the Federal Reserve System, and campaigns on abolishing this monster. It's really rather amazing that more of our lawmakers don't seem to understand or care about this issue. The fact that the value of our money is decided by an elite handful of unelected, unaccountable private bankers meeting secretly in a marble palace ought to be shocking to every American.
The fact that these private bankers, with the help of Senator Nelson Aldrich, wrote the very laws that give them such power ought to have every one of us ready to reach for our guns. Or at least ready to pull the ballot lever marked "Ron Paul." If you think I'm exaggerating, I urge you to read The Creature From Jekyll Island, Secrets of the Temple or Congressman McFadden's Speech then judge for yourself.
3) He wants to get rid of the Income Tax and the IRS. He's not alone on this; Duncan Hunter and Tom Tancredo both support the FairTax, which repeals the 16th Amendment and gets rid of the Tax Gestapo. What's different about Ron Paul is that he wants to replace the Income Tax with nothing.
The FairTax is revenue-neutral, which means the bureaucracy in Washington still gets the same amount of money, they just make it more expensive for us to buy nice things with a progressive national sales tax. Wouldn't a progressive sales tax just put things like computers, cell phones and automobiles further out of the economic reach of the poor, working class and the middle class?
I fully admit that Ron Paul needs to do a better job articulating where the federal government would get it's funding without an income tax, without the Fed, and without tariffs. I know we could use excise taxes or a flat national sales tax on all non-food items to generate revenue, but I haven't heard Paul really address this in any detail.
Update: I apologize most humbly for my ignorance of the FairTax. I was under the mistaken impression that it is a progressive sales tax; this is not true. The FairTax is a flat national sales tax, and while I still don't like the idea of a revenue-neutral tax structure, there is no question that the FairTax would be a vast improvement over our current system. On further reading, I think the FairTax may actually be the perfect vehicle for funding during a transition period to a smaller federal government. My optimistic side thinks that the tax rate could even be lowered as we need less money for the federal budget, but my inner realist (or cynic, whatever) thinks that's about as likely to happen as me winning the lottery, which I don't play.
4) The man has integrity! All the Washington games of vote-trading, vote-buying, special interest groups and lobbyists seem to have had no effect on Dr. Paul. His rhetoric and voting record have been consistently principled over 10 terms in Congress. To deliberately use rabid fan-boy hyperbole, it's like Ron Paul is Frodo Baggins: able to be trusted with the Ring of Power because of his relative immunity to it's corrupting influence. (Ok, so I'm a nerd. Sue me.)
5) He understands that the 2nd Amendment applies to individuals, not militias. (If you disagree with that, please let me know why so I can obliterate your argument with historical facts.) Ron Paul has consistently received A+ ratings from the Gun Owners of America. What can I say, I'm from Kentucky. We like our guns.
6) He is possibly our only chance to stay out of war with Iran. Having already spent more time than I care to in the deserts of the Middle East, and having recently separated from active duty in the Marine Corps, I'm really not too keen on the idea of being recalled to active duty to fight another war in the desert that has nothing to do with our national security.
I was listening to a Ron Paul interview the other day (sorry, no link) where he points out something I hadn't considered before: when we threaten Iran over it's nuclear program (and like it or not, Iran does have the right to use nuclear technology for peaceful purposes such as power, according to the Non-Proliferation Treaty) or we park warships off the Iranian coast, we're helping Ahmadinejad by effectively silencing his opposition. That's hard to follow, let me explain.
Remember the mood of the country from January to October, 2001? The Democrats were convinced that Bush had used foul play to steal the election. The fact that Gore had won the popular vote but lost the electoral college had many on the left wondering whether we even needed an electoral college, and of course there were the dangling chads and functionally-illiterate Floridians. Then, we were attacked. On September 12, 2001, there were no Republicans and Democrats. There were only Americans who were shocked, afraid and mad-as-hell. Those who opposed the president either changed their tune or shut up entirely after we were attacked, at least for a while.
This is what happens when any country is attacked, or under threat of an attack. Centrists and members of the opposition find themselves supporting their leader, or at least remaining silent in their opposition. There are Iranians who do not want to live under the Ayatollah's theocracy. While I don't think we should be supporting them financially or militarily, (see Attack Dogs above) I certainly think that we ought to take away Ahmadinejad and Khomeini's great unifying tool: fear of an attack on Iran by the U.S. If the Iranian government didn't have us there to portray as a menace requiring Iranian unity, they might just be forced to adopt the more democratic reforms of the opposition.
Ok, this ended up being a bit longer than I anticipated. If you made it this far, thanks. Now go spread the word and vote for Ron Paul!