Just scanning the web through various search engines using the string "long hair" I come across lots of stuff. One thing that kept reappearing were these articles by people who, although they had good intentions, basically said having long hair was a sin.
They used a single verse alone to justify what they were saying, and basically stretched it's interpretation to cover what they believed. This verse; 1 Corinthians 11:14.
Now, let me clarify what this verse is about. It was Paul's advice to the people of the church of Corinth. You see, in Corinth at the time, there was a lot of stuff going on, a lot of perversion, and for some reason (don't ask me) the men of the area that were sexually perverted had long hair. Paul wanted the church of Corinth not to grow their hair long for fear they might be mistaken as these perverts. What was said to Corinth was not God's order to the everyone at all times, it was advice especially for the people of Corinth, who lived in the filth.

So who am I to say long hair isn't a sin? Well, I'm not God, so I can't say it's not a sin, but I don't think there's anything wrong with it as long as it doesn't lead you to sin. (I can only think of one way that could happen) There are plenty of references in the bible about long hair as well.
There is of course, foremost in everyone's mind; Samson. Through God Samson's long hair was a source of his strength. He cut it, he lost his strength. To me that seems to me to say Long hair=tough, short hair=weak. (I'm just kidding around) But seriously, Samson's strength was defined by his hair. This of course, probably doesn't mean that if a Christian grows out their hair they're going to become a super hero or anything. But, with God, all things are possible, I mean, if God decided he was going to do for someone living today what he did for Samson, then I'm sure they'd be one tough hombre. No joke. They'd probably be like the ultimate fighting champion if God wanted them to be. But enough about fighting. Let me lay down some verses: Numbers 6:1 through 6:5. These few verses are what God told Moses about the vow of a Nazarite. The just of what he said is basically that these people shouldn't eat grapes, raisins, or drinks strong drinks like wine. However, the real kicker comes in 6:5, where God says "All the days of the vow of his separation there shall no razor come upon his head: until the days be fulfilled, in the which he separateth [himself] unto the LORD, he shall be holy, [and] shall let the locks of the hair of his head grow."
Which means exactly what it says; "Tell them to let their hair grow long." Now, I'm not sure how the vow of the Nazirite fits into modern Christianity, but if people who set themselves aside for God were told to let their hair grow long, I honestly don't see how it could be so bad for a Christian to have long hair today.
Also, there's my biggest argument of all: God looks at our heart, not our outward appearance. I refuse to believe God's going to "condemn you to Hell" as one article I read seemed to imply, for having long hair. That's religion plain and simple. If you want real answers, get the truth from God. He could care less whether you have long hair, short hair, or no hair at all. So long as it doesn't hinder your relationship with him and his son, Jesus Christ, it's your hair, do something fun with it.