If you're looking for anime that've inspired great novels (or vice versa), my top pick is the 'Monogatari' series. Originally light novels by Nisio Isin, the anime adaptation captures the same witty, dialogue-heavy charm with surreal visuals. The wordplay and character dynamics are even richer in the written form—especially 'Kizumonogatari,' which dives into Araragi's backstory with almost poetic violence. Another gem is 'The Garden of Words' by Makoto Shinkai; while the anime is a gorgeous 46-minute film, the novel expands on the protagonists' inner turmoil, adding layers to that rainy-season romance.
For something darker, 'Puella Magi Madoka Magica' has a novelization that amplifies its psychological horror. The anime's twists hit hard, but the prose lingers on Homura's despair in a way that still haunts me. And if you love world-building, 'Log Horizon''s light novels are a must—the anime skims over the politics of its trapped-MMO world, but the books make every guild negotiation feel epic.