For real LEGO enthusiasts, IKEAhacking is like building with LEGO. So why not combine both? An easy way to do this is using LEGO bricks for IKEA door or drawer knobs.
What you need is a LEGO brick, a 30mm M5 screw and the spacer washer – mine comes from a leftover plug of a PAX shoe shelf. Put the screw in the back side of the door, put the spacer washer on the screw on the other side of the door, then screw on the LEGO brick. The spacer washer allows you to easily grip your new door knob.
You can also mount the brick directly to the door without a spacer washer, but you have to use a shorter 25mm screw and a normal washer (without the washer the brick gets damaged by the screw). With this version, it is a little harder to grip the knob, but works just as good.