You can now download cydia for iOS 8 and install it manually.
If you have already jailboken your iOS 8 device with Pangu, you can now install Cydia too.
Please note that you need to do this manually, and that not all cydia tweaks are compatible with iOS 8 for now.
download: Cydia version 1.1.13 (553B)
description: Cydia version 1.1.13, used for Pangu 8 jailbreak.