How often have you found yourself tongue-tied in not knowing how to answer Muslims? The internet is rapidly becoming the best source of apologetics available, provided that you know where to look.
If, doubting the Qur'an's claim to divine inspiration you are asked to 'produce a sura like it' (Sura 2:23) you will find many suras fitting the bill posted at http://members.aol.com/suralikeit/newest.htm. Muslims who say that they would convert to Christianity if you could show them a contradiction in the Qur'an should similarly be referred to http://www.answering-islam.org/Quran/Contra/ for a comprehensive list.
John Gilchrist's excellent resource on answering Islam 'Jam' Al-Qur'an' is now available at and for general Christian apologetics you can't do much better than the 'Christian Apologetics bookshelf'.
Islamic Sites
Among Muslim sites http://www.al-muslim.org/ is one of the best so far. The 'Frequently asked Questions' section, although designed to answer Christianity is titled 'Muslims and Islam'. Those preferring special effects to content should visit the site of the Islamic Society of RMIT (Australia)
Extensive other Islamic links, including Qur'an and Hadith sites, can be found at http://www.answering-islam.org/L_islamic.html and those wanting cheap Islamic books should shop at http://www.xmetric.com/islamicbooks/