Some common NPN transistors are the 2N2222 and 2N3904. Look at the part numbers carefully as PNP transistors look the same! Most of the time, an NPN transistor will work for you. Here is a comparison of NPN vs PNP:
These little guys can switch incredibly fast but have lower maximum ratings than TIP120’s – max voltage 40V, max current 200mA (datasheet).