G-portal: 50% off for all pre-paid servers (up to an year): https://www.g-portal.com/en/news/blackcontrollerday-50-discount-430
GTXGaming: 50% for 1 month only: https://www.facebook.com/gtxgaming.gameservers/photos/a.126064067459337/2772680502797667/?type=3&theater
ServerBlend: nothing on the main page but quite a few coupon sites seem to offer 15-20% off discount codes.
LogicServers: 33% off for the first period: https://logicservers.co.uk/cyber-sale
Zap-Hosting: 50% off https://zap-hosting.com/de/gutscheinportal/
Feel free to add to the list