I'm not sure which ones are the absolute best, but on AO3, you can sort the search results by kudos or bookmarks. The ones with high numbers of these are usually quite popular and might be really good 'fleur wants harry fanfiction' stories.
You can try some popular fanfiction websites like Fanfiction.net or Archive of Our Own (AO3). Just search for 'fleur wants harry' on their search bars and you might find relevant stories.
Often, Luna Lovegood can be found in such fanfictions. Her unique and dreamy nature could bring a different dynamic to the harem. Neville Longbottom might also be involved in some way, perhaps as a friend who supports the harem and helps them out in times of need. There could also be some foreign exchange students or magical creatures in human form that end up in the harem for various reasons.
At first, their relationship might be a bit strained. Harry is used to his own space and friends, and Fleur has her own circle. But as they live together, they'll start to respect each other's differences. For example, Fleur might be more flamboyant in her magic use, while Harry is more practical. They'll start to see the value in each other's approaches and become closer friends.
One possible reason could be that Fleur sees Harry as a powerful and important figure. In the wizarding world, Harry is the famous Boy Who Lived. Fleur might be possessive because she wants to be associated with his fame and power. Also, his bravery and skills could be attractive to her, making her want to have him all to herself in the fanfiction world.
Hermione would probably be a bit skeptical at first. She might worry that Harry is rushing into things. But once she sees how happy they are, she would be supportive. Ron, on the other hand, would be more accepting from the start, especially if there are good feasts at the wedding.
Often, Harry's sense of responsibility grows. He starts to see the marriage contract as not just a burden but also an opportunity to create a new life for himself and Fleur. Fleur's personality may develop in a way that she becomes more protective of Harry. For example, when they face opposition from the wizarding community about their contract, she stands up for them. She also might help Harry to overcome his insecurities about being in a relationship with someone as glamorous as her.
At first, they might be at odds with each other. Fleur could think Harry is too impulsive, while Harry might find Fleur a bit too haughty. But then, when they are forced to work together on a mission, they see the good in each other. Fleur realizes Harry's selfless nature, and Harry sees Fleur's intelligence and determination. This new - found respect leads to a romantic relationship and ultimately marriage.
A less common but still interesting trope could be the 'time - travel' trope in relation to them. For instance, if Hermione were to go back in time and meet a younger Fleur, or vice versa. This could lead to all sorts of interesting plot developments as they interact with the past or future versions of each other and the events in the wizarding world.
One plot idea could be that Fleur starts off subtly trying to befriend Hermione. She might invite Hermione to various Beauxbatons events under the pretense of cultural exchange. Then, as time goes on, Fleur becomes more possessive, getting jealous when Hermione spends time with Harry or Ron. Another idea is that Fleur discovers Hermione's unique magical abilities and wants to keep her close to learn from her and also have her all to herself. Maybe she tries to isolate Hermione from the Hogwarts crowd.