The first bit of advice was this:
I'd just take a copy of 'On the origin of the species' ( hardback) and smack any proponent of ID over the head with it :)
Another commenter said:
Cordyceps fungi and various parasitic insects (i.e. wasps). No way they could have been 'designed'.
I weighed in, as is my wont, with these two comments. (I've altered a word here and there for clarity). Perhaps it might be useful in your context...
I'm a Christian who believes the universe was designed (in one sense every Christian believes in intelligent design - since God's quite smart) but I don't like ID as a movement, cos the Christian story is actually that A) Creation is *fallen* and B) God is known, not by studying irreducible complexity but by seeing Him in the face of Christ.
That said, ID proponents are not dummies (some are, many aren't). And when they raise tough questions about thorough-going naturalism, they should be heard. How do systems increase in informational content without an intelligent input? That is a good and vital question? How can natural selection account for irreducible complexity (systems where incremental developments could never add up to the system as a whole because the individual stages don't add survival value)? That is a good question and needs more than a dismissive answer. Like I say, I'm not any kind of proponent for the ID movement, but they do raise vital scientific questions that shouldn't simply be dubbed stupid.
On another note, for the Christian, parasites are a brilliant testimony to the Bible's story. Parasites are secondary things that come along and spoil an original and ultimate good. That is precisely the Bible's picture of good and evil. There is an original and ultimate good (God) spoiled by something secondary and derivative (evil).
Like I say I'm not a fan of the ID project - but... Remember where the whole discussion begins. It begins with the undoubted and gob-smacking *appearance* of intelligent design. Everyone agrees that the world looks designed. A biologist might come along and say "I've found a mechanism that accounts for that appearance." But even if the mechanism has tremendous explanatory power (and natural selection does), remember:
A) Good science involves questioning paradigms, and IDers should be allowed to question "Does this mechanism really explain this and that?" Irreducible complexity and the information problem are some *excellent* questions to ask of the materialistic paradigm. It's not good science to ridicule that questioning. It actually starts to sound like a power play.
B) Even if we grant that Darwin has sewn up 'the origin of the *species*', there are still three other origins questions that are at least as pressing: origin of the cosmos, origin of life itself, origin of consciousness. You might want to argue that natural selection explains all of these, but at that point I recall the old saying: If all you've got is a hammer, everything starts to look like a nail. Natural selection is an excellent hammer to be applied to certain features of the natural world, but I'd seriously question its ability to explain everything. Darwin's finches are fascinating and tell us much about evolution - it's quite a stretch to make them explain the cosmos!
C) Remember that discovering a mechanism says precisely Nothing about the existence of a Maker. It's useful to know the workings of an internal combustion engine, but no matter how comprehensive the knowledge, the existence of Henry Ford is an explanation beyond the wit of reverse-engineering. Mechanism and Maker are two different questions.
D) Remember where the conversation begins. It begins with everyone agreeing that the world looks eerily like it's designed. Even if you come up with an elaborate mechanism and provide convincing answers to all objections, the simplest explanation (i.e. that it *is* designed - and natural selection is one mechanism among many) is a perfectly reasonable position to take! Those who ridicule it are betraying the rational, scientific ideals they claim to be upholding.
Like I say, I'm not an IDer, I'm just a Christian, but I look on the debate with interest.