Well, we have modern examples of plant speciation. Some where two plants, through a freak occurrence, make a plant species that can't breed with the species that created it. Ergo, brand new species.
Complex animal speciation takes a much longer time and is generally thought to be gradual - at least in regards to the average human lifetime. However, that doesn't mean that evolution is not provable or incorrect. FIrst off, you have DNA - which was discovered long after the evolutionary theory was first described. DNA validates evolutionary theory in a manner that was inconceivable to someone during Darwin's time. The very fact that we can tweak genotype to affect phenotype, find relatives, identify/clear suspected criminals etc. etc. is all based on evolutionary theory.
The fossil record also supports it. The fossil record shows that mammals first lived on land. However, we now have mammals that live in the sea - like whales - who haven't been around all that long. Putting aside the fact that the foundation of evolutionary theory would suggest that we are most closely related to whales than fish genetically (which is true) even though a couple hundred years ago it would be argued otherwise because there shouldn't be any relationship/lineage between two different species and, well, a whale looks much more like a fish than a human. Evolutionary theory also makes a prediction (that has absolutely no reason to be true if evolution is false). If mammals first lived on land, and a whale is a mammal, then there, at some point, must have been a whale-like ancestor with legs. It wasn't that long ago that this fossil was found. A whale with vestigial legs.
To deny evolution, is to deny everything that science is about.