I don't think we're seeing speciation here, yet, but it's still very interesting: the bodies of snakes in Australia have changed in the last 70 years to adapt to the introduction of the toad down under. The smaller heads and longer bodies keep them from eating the toads, which are poisonous.

The toad situation in Australia is a classic example of the central thesis in one of my absolute favorite popular science book ever, Out of Control, which argues that the environment is far more interconnected, complicated, and chaotic than we generally think. Seemingly minor changes, like introducing cane toad to Australia to control agricultural pests, lead to unpredictable results -- the overrunning of Australia with toads, the threat to indigenous animals and wildlife, and, now, the beginnings of evolutionary change to deal with it.

Basically, OoC argues that the Biosphere is a fine-tuned, highly complex machine, and we have absolutely no idea what the effects will be when we muck around it. In this case, in few thousand years, Australia will probably be in balance again -- but in other cases, we may be doing significant, permanent damage to our ability to live on this planet, without even realizing it.