Amongst various of my big influences, one of the earliest was Francis Schaeffer. I went to see the "How Should We Then Live?" series of films when I was about 10 with my dad - and they were way over my head. I happened across the book in the public library when I was an undergraduate, and it made loads of sense. I later rented the videos from L'Abri, and then got into his other books - particularly the "Essential Three" - The God who is There, He is There and He is not Silent, Escape From Reason.
Francis Schaeffer has had a vast influence on the shape of intelligent Christianity in the last 40 years - perhaps with C.S.Lewis one of the key Christian thinkers of the 20th Century.
One of his interesting predictions (from the liberal 70's!) is that people would be prepared to sacrifice almost any freedoms for personal peace and prosperity. Thought-provoking in the era of the Patriot Act and the proposals in the UK to strengthen detention without trial.