 If you liked Fate/stay night |  ...then you might like Shitsurakuen |
Both involve female knights. Also, Shirou swore to become a protector of justice and Sora swore to become a knight of justice. Both manga involve a "game" of some sort, while Shirou fights in a game for the Holy Grail, Sora fights in a game called Exaclan. The only difference is that Shitsurakuen has a shoujo-ai + harem hint, although they both include shounen, action and fantasy. If you liked Fate/stay night then it is likely that you will like Shitsurakuen.