Well since evolution is simply genetic mutations, we see it fairly frequently. If you go into an exotic, tropical area, you're likely to see many different types of bird who have all evolved slight differences from each other, yet all have an obvious common ancestor that may not be that far removed, or in fact may still actually exist. Migratory patterns and changes in landscape spark the encouragement of genetic manipulation to meet with the needs of the new terrain, so when some animals migrate to another area, you may see slight changes in a few generations in the sect that migrated, and no change in those who did not migrate. Of course, we don't have absolute evidence of things such as single-cell to multi-cell organisms, but there are things that we know. For example, the question of life emerging from water. There are certain types of fish that exist even today that actually have legs.
Edit: I'm sure somebody else could give you better examples and explanations, as this is not exactly my forte.