Good science is predictive. The Theory of Evolution is no different. Below I list some of the predictions made by Darwin himself.
1-When Darwin formulated his theory the prevailing scientific opinion was that the earth was only thousands of years old. Calculations done by Lord Kelvin based upon the possible limit for the age of the sun put the age of the earth at no greater than 20-40 million years. Darwin said that the earth would have to be at least hundreds of millions of years old for his theories to be true. Other scientific disciplines, including astronomy, geology, and radiometric dating have proved that Darwin was correct. Darwin's theory was the first piece of science to predict an earth that was this old.
2-At the time of Darwin the dominant scientific view regarding the inheritance of traits was that traits would be diluted in subsequent generations. For instance if a person was extra tall, over time his offspring would generally reduce in height towards the pre-existing average height. A tall human and short human would produce a medium sized human. For Darwin's theories to be true there had to be a means of retaining desired variations. The re-discovery of Gregor Mendel's work has confirmed Darwin's view that traits are not diluted, and genetics has helped explain why this is the case. This again was a bold prediction that contradicted the current views.
3-Based upon studies of human anatomy as well as the anatomy of other primates, Darwin and Huxley predicted that humans and other apes shared a common ancestor that most likely originated in Africa. DNA studies have shown that chimpanzees are our closest evolutionary relative. Many fossil finds in Africa, including such animals as Australopithecus africanus have confirmed Darwin and Huxley's predictions. Australopithecus afarensis is the oldest hominid species ever discovered, and was of course discovered in Africa. What makes this prediction even more amazing is that no hominid fossils had been discovered while Darwin was alive.
4-When Darwin formulated his theories fossils had not yet been discovered dating from the pre-Cambrian era. His theories required that this era would have to have been swimming with life. There must be life in this time frame. In the last 50 years abundant fossils have been discovered from pre-Cambrian eras.
Other predictions of the Theory of Evolution
1-Humans have 23 chromosomes, whereas other apes have 24. If we share a common ancestor with the other apes then two of our chromosomes must have fused to form one. A chromosome has what is called a telomere on either end, which functions to keep the chromosome from falling apart. Kind of like applying heat to the end of a rope to keep it from fraying. The interior of the chromosome has what is called a centromere. These are necessary for chromosome duplication. If humans and other primates share a common ancestor we should find that one of the human chromosomes looks like it is really two chromosomes butted up against one another. This new single chromosome would have a telomere on either end, two centromeres, and two more telomeres at the very center. So what do we see? Human chromosome #2 has exactly these features, with one of the centromeres deactivated.
2-Most mammals manufacture their own Vitamin C, whereas humans must acquire Vitamin C from food sources. If evolution is true our DNA should reveal that we have the genetic mechanism to create our own Vitamin C, but this mechanism has been de-activated for one reason or another. And of course this is exactly what we find. A mutation has de-activated the DNA that allows us to create or own Vitamin C. Furthermore other primates likewise have the identical de-activated Vitamin C manufacturing sequence.
3-As I discussed on the radio with Bob Dutko, there are certain viruses that transcribe there own viral DNA into the cell they have invaded. These are called retro-viruses. If a retro-virus attacked reproductive cells, then the offspring that result would retain the viral signature natively. Evolution would predict that animals more closely related to us would share more virus signatures in common with us, and these virus transcriptions would occur at the corresponding locations within the genome. Animals less closely related to us would have less. What does the DNA evidence show? Exactly what the theory of evolution would predict. To this point 7 shared ERV's have been identified between humans and chimpanzees. Less with other, less closely related animals. For instance, mice and humans share a common ERV. As evolution would predict chimpanzees also have this virus. Mice and humans share an older common ancestor, so you wouln't expect mice and humans to share an ERV that chimpanzees don't also have.
4-The Theory of Evolution predicts that four footed fish like creatures must have emerged about about 375 million years ago in the Devonian period. Rock of this age was exposed due to tektonic movement in Canada, so geologists went there looking for a fossil of a four footed fish like creature. And this is exactly what they found. It is called Tiktaalik.
5-Evolution predicts that whales were once land animals that drank fresh water. They moved first to fresh water, then to salt water. It is possible to determine if an animal drank fresh or salt water by measuring the slightly different oxygen isotopes that result. Sure enough the two oldest species of whale discovered contain oxygen isotope concentrations that show that they were fresh water animals. The later specimens were salt water animals.
What non-trivial, unexpected predictions has Creationism produced? None that I know of.