Here is a nice little collection of pages about current evolution in action in the streams and pools of Trinidad.
Scientist John Endler studied the habitats of guppies to determine why guppy coloration varies in different locations. If bright colors made guppies more conspicuous to predators, why should males be colorful at all? He found that there are two forces for natural selection at work for the guppies.
This is from a long overdue series about evolution on PBS. Faq about evolution.