Transistor

Low Cost Universal Battery Charger Schematic

MCU driven transistor

probably best solution
Intelligent NiCd/NiMH Battery Charger
More information on this solution.
Intelligent Universal Battery Charger

LM317 and transostor

Switchless NiCd-NiMH Battery Charger

Transistor and op-ampflier

NiCd charger with independent discharging

Resistor

Nabíječ NiMH / NiCd s automatickým vybíjením

Need to be study

Automatic nimh battery charger circuit