Here's a handy 3-pack of 4cm x 6cm Proto-board PCBs in Adafruit Black. Both sides have a black silkscreen with some row/column markings. Note that these don't have any traces between the PCB holes, you would normally bend over a thru-hole lead to create connections. They're also good for just plain mechanical work because they are made of strong FR4.
There are also four mounting holes so you can attach the PCB to your project box.
These are affordable and of good quality so we decided to put them in a pack of 3.
Contains 14 X lines and 20 Y lines totaling 280 holes.