In the Last Battle, at the end of the book, Aslan actually transforms into Christ in front of the now grown up children. I'm with you, I don't think there was ever any doubt that Aslan = Christ.
BTW, my kids Christian middle school has Aslan as its mascot. They're taking the entire school to the movie next week. I was at the Steven Curtis CHapman/Mercy Me Christmas concert earlier this week, and they played a music video with a trailer from the movie. Looks AWESOME!
here's a cool trailer for the movie.
http://www.narniaweb.com/trailers.asp