Regulators are very useful devises for every hobbyist.
The can sever two functions either as Voltage Regulators or as Current(I) regulators.
Variable Regulators
LM317 1.25 to 37 Volts at 1.5 Amps
LM117 1.2 V to 25 Volts at 0.5 Amps
Fixed voltage regulators
7805 5 Volt 1 Amp also the 78L05 (100mA)
7809 9 Volt 1 Amp
7812 12 Volt 1 Amp
Switch Mode Regulators