My friend once told me a story about how his best friend helped him when he was going through a tough time at school. His friend stood up for him against bullies and helped him with his studies. That's a real sign of true friendship.
I know a story of two friends who got separated due to family relocation. But they kept in touch over the years. When one of them fell ill, the other one traveled across the country to be with him. Their unwavering bond despite the distance and time is a great example of a beautiful friendship.