Some well - known ones could be 'In Another World with My Smartphone'. It features a harem - like situation where the protagonist is surrounded by multiple female characters in a guild - like setting in a fantasy world.
Another might be 'The Rising of the Shield Hero'. While not strictly a 'harem guild' in the purest sense, it has elements of a harem with characters in a guild - like environment. The protagonist, Naofumi, has a group of female companions who play important roles in his adventures.
One popular 'favorite harem light novel' is 'Date A Live'. It has an interesting premise where the protagonist has to go on dates with spirit girls to prevent them from causing disasters. Another is 'The World God Only Knows', which features the main character using his knowledge of dating sims to capture the hearts of various girls. And 'High School DxD' is also well - known, with a story full of action and a harem of different female characters around the main male lead.
One popular 'slave harem light novel' could be 'How a Realist Hero Rebuilt the Kingdom'. It has elements of a harem where the main character has multiple female characters around him. Another might be 'Overlord', where the main character also has a group of followers that could be seen in a harem - like context. And 'The Rising of the Shield Hero' has a harem - like situation develop around the main character as well.
Well, 'The Rising of the Shield Hero' can be considered. The protagonist is summoned to another world, which is a typical isekai tensei situation. And he has a group of female companions who support him in different ways, which gives it some harem - like vibes. Also, 'Konosuba: God's Blessing on This Wonderful World!' is very popular. The main character is sent to a fantasy world (isekai) and he has a group of girls around him, which is a classic harem setup in light novels.
One popular title could be 'In Another World's Labyrinth, My Harem Awaits'.
A third example could be 'Kamigami no Asobi'. In this light novel, the female main character is transported to a world where she meets various male gods, forming a reverse harem situation. The story is rich in character development for both the protagonist and the male characters around her, which is characteristic of this type of light novel.
One popular 'isekai harem novel' is 'No Game No Life'. In this story, the two main characters are transported to a different world filled with games and rules. They encounter various female characters, and a harem - like dynamic develops as these characters are drawn to the protagonists' intelligence and unique abilities.
One popular'renai harem game novel' could be 'Amnesia: Memories'. It has an interesting story with multiple love interests for the main character. Another might be 'Diabolik Lovers' which is known for its unique take on the harem genre in a rather dark and supernatural setting. And then there's 'Uta no Prince - sama' where the main character is surrounded by a group of talented and charming male characters in the music industry.
A few 'isekai tensei harem novel' titles are 'Sword Art Online'. In the ALO and other arcs, Kirito has interactions with multiple female characters that have some harem - like qualities. And 'Log Horizon' is also relevant. Shiroe, the main character, is in a world full of different races and characters, and he has relationships with several that can be seen in the context of a harem in the isekai setting.
The harem aspect offers a sense of wish - fulfillment. Readers can imagine being in the shoes of the protagonist surrounded by multiple interesting characters, usually of the opposite sex. In the guild setting, it adds an element of adventure and camaraderie. For example, in a typical 'harem guild light novel', the characters might go on quests together, and the different personalities in the harem add drama and romance to the story.
One popular 'farming light novel' could be 'Farming in Another World'.