The kind folks at Monergism have seen fit to offer for free an ebook by Steve Hays. I haven’t read it yet, but it looks like it contains some good stuff.
Poke around this link – there’s some other good stuff there too!
“Helpful answers to the most common objections of postmodern skeptics and atheists. Steve Hays demonstrates that engaging skeptics presuppositionally is perhaps the most persuasive way to engage them, especially in the current environment.”