Brother HL-L2340DW printer cartridges
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.