I believe that some knowledge of philosophy is important for everyone. It is especially important for those interested in apologetics. That is not to say you have to be a philosopher to be an apologists, but the more you know about the basic concepts, the better.
I recently read a nice little introduction to philosophy called Ultimate Questions: Thinking About Philosophy written by Nils Ch. Rauhut. I quite enjoyed this book. It is written with the beginner in mind and makes no assumptions about previous philosophical knowledge.
The topics in the book include logic, epistemology, free will, personal identity, mind/body problem, existence of God and ethics. Rauhut presents the major theories for each of these areas and gives suggested reading for further study. Every theory is presented with strengths and weaknesses, giving the reader the opportunity to work through their own beliefs,
This is not a book on Christian philosophy. Some of the ideas presented on the existence of God will raise some red flags for apologists. Still, I think that Rauhut is fair in his presentation and that the book is helpful for Christians.
If you are looking for a nice introduction for those just starting to think about philosophy, this is a good choice.
