Christianity is not a religion
The claim is supported by various justifications:
- Christianity is a relationship with God
- Christianity is a moral code
- Christianity is a philosophy 
- Christianity is based on faith not works 
- Christianity requires faith 
- Other religions are man made to explain the world, Christianity is from God. 
None of these arguments preclude Christianity from also being a religion.
Another interesting argument is that Jesus was against religious institutions of his time. Therefore, Christianity is anti-religious. Therefore, Christianity is not a religion.
- "What separates Christianity from other religions is the fact that it's actually not a religion. Jesus was the most anti-religion person that ever lived. "
An argument from the etymology of the word "religion":
- "The Latin word from which the English word "religion" is derived means "to bind up." Jesus did not come to bind us up in rules and regulations or rituals of devotion, but to set us free to be man as God inended. [sic] "
Christianity fits any normal definition of religion. The argument that Christianity is not a religion revolves around equivocation over the word "religion". Attempting to redefine the word "religion" is intentionally misleading.
Christians refer to Christianity as a religion
"The Christian religion was moreover commonly charged with being the cause of the calamities that so frequently befell the State"
"For, true religion is that by which the soul is united to God so that it binds itself again by reconciliation to Him from whom it had broken off"
- "Yes, Christianity is the one true religion. "
"[...] where the Holy Ghost dwelleth, He will not suffer a man to be idle, butstirreth him up to all exercises of piety and godliness, and of true religion [...]"
"Pure religion and undefiled before our God and Father is this, to visit the fatherless and widows in their affliction, and to keep oneself unspotted from the world."
Responding to "Jesus was anti-religious"
This is simply explained by Jesus being against some aspects of religion - specifically institutional religion. To say he was anti-religious is a hasty generalization.
Also, Christianity generally ignores the teachings of Jesus when it comes to religion. For instance, public prayer is condemned by Jesus Matthew 6:6 . Even if true, the supposed fact that Jesus was anti-religious does not prevent Christianity from being a religion. For this reason, Christianity is one of the most hypocritical religions.
Argument from the etymology of the word "religion"
Other religions make this claim
Christianity's claims to uniqueness are ironically shared by other religions:
- "Buddhism is not a religion because, first, the Buddha is not a 'supernatural being power.' "
- Christianity is not a religion, RationWiki