The intelligent design argument counters evolution by claiming some processes are irreducible and couldn't have come about piecemeal. Commonly a mousetrap is used to illustrate this, being an object that couldn't exist without having been consciously designed for its purpose. A reducibly complex mousetrap [via Bifurcated Rivets] counters intelligent design with a possible evolution path. It could be a more convincing article, though, if it could show why each intermediate step was more effective than the step before.
Why is evolution such a controversial topic? Things around us so obviously and blatently change with their environment. Whether you call it population shift or natural selection isn't important. Similarly, whether we've correctly identified the evolutionary mechanism isn't important. But the concept itself - that complex things have come from less complex things - even if we don't know exactly how - why should that be under dispute?