Probably the most familliar writing instrument to most people, ballpoint pens are everywhere. While a ballpoint does require some pressure to make it work, most good quality modern ballpoints write quite smoothly, and can put down more solid lines, and better colours, than older or cheaper models.
Despite the introduction of liquid ink and gel ink rollerballs, ballpoints are still the most-used type of pen, for some good reasons. Ballpoint pens are amazingly reliable, and if they do stop working, usually only need a bit of scribbling to get going again. Choices are almost unlimited, at high or low price ranges. All but the cheapest ballpoints are refillable, and refills last a long time - both in terms of writing length and shelf life.
If you're looking for a simple 'stick' ballpoint, you can't go far wrong with the classic Staedtler Stick. If you prefer retractable pens, the Zebra Z-Grip offers great quality for a low price.
For a more luxurious ballpoint, it can be worth looking for something that takes standard refills - many full-size ballpoints take Parker-style refills, giving you a huge range of options for refills, with a large range of colours and tip sizes, from extra-fine to extra-broad. Compact pens often use 'D1' multipen ballpoint refills, again giving you a good choice of brands and colours.
The ubiquity and popularity of ballpoint refills means that it's the default choice for most designer pens - the sheer variety of ballpoint pens is amazing. Try Caran d'Ache and Lamy at the mid price points; and Graf von Faber-Castell or Porsche Design for some luxury options.