One is Audie, which turns written books into high-quality audiobooks using natural-sounding voices. You can pick from more than 50 different voices, including different accents and speaking styles, and customize the voice by cloning your own. It's relatively cheap, with tiered pricing for different levels of use, and it produces files compatible with Amazon and other major platforms.
If you need more languages and voices, check out Narration Box. It supports more than 140 languages and accents and has a library of 700+ AI narrators. It's got advanced features like context awareness, emotive styles and long-form support, and flexible pricing, including a free tier. That makes it a good option for a wide range of audiobook production.