This is a good question which I will attempt to answer. I would say the best christening gift you can give a child is your support. That is your love and prayers throughout his or her life and helping them find their faith in God.
Keeping that goal in mind, there are certain gifts which will help achieve that goal.
BiblesThe Word of God is always an appropriate gift regardless of age. Sometimes a pictorial Bible will help the child grow in faith while learning the stories of God's Children. What I like about this gift is that they can continue to use the Bible when they have children of their own.
For confirmed young adults and adults who were not baptized as an infant, a NIV or even a NAS Bible are great translations using present day expressions and terminology. These make them easier to read and understand especially in a changing world.
If you want to keep with one of the oldest English translations, stick with the King James Version. This Bible was commissioned in the 1600's and uses the "olde" style of English.