Sony let me unlock my Xperia Z. They also release the drivers to their hardware to the open source community. Well worth supporting this effort when you next choose a handset.
Oppo goes as far as supporting development of CyanogenMod and ParanoidAndroid ports for their devices and are releasing a device in partnership with CyanogenMod.
The Nvidia Shield is Nexus-level friendly: it's just fastboot oem unlock, no special keys or APKs or anything. It's also an incredibly nice device. (I wish Nvidia made phones...)
Moto, Samsung, HTC. All three offer Developer Edition devices which are easily bootloader-unlockable on all carriers.