Both of these get better customer reviews than the Brother brand cartridges that cost twice as much (and apparently aren’t as “high yield” as they claim).

OfficeWorld replacement toner cartridge 2-pack, compatible with the Brother TN-660 cartridge, is cheaper per cartridge.

JARBO replacement toner cartridge 3-pack, also compatible with Brother TN-660 but costs more per cartridge. Reviews are equal to the OfficeWorld.