When he was young, Shiro had the misfortune to be in the middle of a huge disaster that killed his parents. He was adopted by man who rescued him; a man who also happened to be a user of magic. Shiro was taught some of the basics, and has trained through the years but never had much success at using magic. Still, he trains hard to one day become someone who can save people: like his adopted father.
Years later Shiro attends high school. One day on his way home, he witnesses two people with god like powers clashing in the school yard. These beings are known as servants: spirits of those who did heroic deeds in their past life. Having seen something he shouldn't have, Shiro is chased down. Just as things look hopeless for him, Shiro inadvertently summons his own servant which saves him. Her name is Saber, and she claims him to be her master in the war to obtain the holy grail. Seven such masters exist, but the grail will only grant a wish to the one left standing.
Shiro is unsure if he should fight, but many people could be hurt with something as dangerous as the grail war. Isn't this the opportunity he's waited for? A hero will surely be needed.
Fate Stay Night is a visual novel created by Typemoon (also known for the very popular Tsukihime) Fate Stay Night went on to become one of the best selling visual novels in Japan. It's also spawned a TV series, a movie, a prequel and even a magical girl spinoff.
I'm not sure any anime version lived up to the visual novel, but I figured the concept and characters alone are cool enough for a website.