Here's a handy 3-pack of 3cm x 7cm 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 10 X lines by 24 Y lines totaling 240 holes.