The BIC Cristal - probably the best-known ballpoint in the world. It's inexpensive, it's reliable, it writes really smoothly and it's safe to say there can't be many households without at least one Cristal stuffed into a kitchen drawer.

This is the Cristal Exact. The clue is in the name, as it has a super-fine tip that writes a 0.7mm line. Perfect for when you need a bit of precision.