Ken miller explained this using the mousetrap. Behe said the bacterial flagellum was irreducibly because, like a mouse trap, if one part was removed it failed to perform it's function. ken miller shot this argument to pieces by wearing a mouse trap with only 3 parts as a tie clip to court. Does it's perform the function of a mousetrap? No. Does it perform a function which could be selected for and considered "beneficial"? yes.
Evolution is not testable - Every new fossil dug up, every genome sequenced, every new species discovered, every new simulation run is a test of evolutionary theory. If what we discover doesn't fit in with what evolution predicts then evolution is wrong. In the 150 years it has been around not a single new discovery, Including DNA and genomes which weren't even known of in Darwin's time, Has told us anything other than what we would expect to find if evolution were a fact. They all end up telling us the exact thing which we would expect to be true if evolution was a fact. The EXACT thing we would expect.
To prove it wrong just discover something which should not be true if evolution is right. I'll help you: The gene for feathers in humans or a chicken in the Precambrian.
There is evidence against evolution - No there isn't. There are poorly understood, fallacious arguments which are parroted, But not a single discovery which should not be true if evolution is a fact. Like i said, Find something which invalidates evolution, like the gene for feathers in humans of a Precambrian chicken; something beyond the flawed probability arguments and baseless assumptions. Find us something real, something tangible, Which should not exist if evolution were true.
Evolution has not been observed - At all levels evolution has been physically observed. Everything from new bio-synthetic pathways and speciation to variations of features in a population due to natural selection.

Even in the short time humans have been here we have changed, through selection, wolves into dogs and teosinte in to corn and we have caused the emergence of pesticide resistant insects and even the formation of a bacteria which eats nylon, something which has only existed for 50 years. Even the humble banana which ray comfort claimed was the "atheists nightmare" only exists because we cultivated it. Humans invented the banana through selection. This is what a wild banana, ya know, the one your god made, looks like.
All mutations are bad - Most mutations actually have no effect and sit happily in the genome not causing any problems. Every person is born with around 200 mutations. We all have 200 genes not found anywhere in our lineage. Some are bad, granted, But those organisms generally die off and so the mutation isn't propagated. The good ones, like a mutation that causes thicker hair growth in cold climates, rapidly propagate throughout the species. Examples of good mutations can be seen in antibiotic resistant bacteria, pesticide resistant insects of drug resistant HIV. Sure they suck for us, But for the organism concerned, they are beneficial mutations.
The probability of cells spontaneously forming is too low - Cells, like all life, Slowly evolved. The first cell was nothing at all like the cells we find in modern day organisms. The first cell would have been nothing but a self replicating molecule, And we have created those in a lab.
No transitional fossils have ever been found - This argument is so weak and out of date even the mouthpiece of young earth creationism, AIG, warns it's follows not to use it. The fact is we have enough transitional fossils to tie together all the species in the class of eumetazoa. We even have transitional forms alive today. Cut open a snake and you'll find a pelvis, a whale and you'll find vestigial legs. Even humans have a vestigial flaps in their eyes which are remnants from reptiles (if you want to see it it's right near your tear duct) and smaller mammals (the tiny lump on your outer ear). we even have about half a dozen pre-human hominid fossils depicting our own evolution since we departed from the branch which lead to chimps, gorillas and baboons.
Speciation has never been observed - Another which AIG advises it's followers don't use. Speciation has been observed in everything from flies to plants. Search "observed speciation" for countless of documented examples.
Evolution violates the 1st law of thermodynamics - Evolution does not operate within a closed system and as such is not subject to the laws of thermodynamics.
Evolution violates the 2nd law of thermodynamics - Same as above, plus; The increase of complexity gained by evolution comes at the cost of the decrease of order of the sun. As the sun "dies" the energy expended comes to earth and is used by organisms to grow.
A denial of evolution - however motivated - is a denial of evidence, a retreat from reason into ignorance; Dr Tim D White
inspired by cdk007