To select a gift means taking a moment to think about that person--his likes and dislikes, hobbies, people he admires and so on. Selecting a gift for a priest is no different from giving a gift to any other friend or family member except that, due to the fact that he is a priest, there are certain items that would be useless and perhaps offensive.
All Catholic priests share certain things in common such as living a celibate life, uniforms, abstaining from luxury items and dedicating their life to the church. Getting a gift that is for a married couple or family with kids would be, at best, taken as a joke and, at worst, greatly offending the priest. Take into account anything particular about the person you want to give the gift to. Is he focused on missionary work, hospital chaplaincy, teaching or family counselling? Based on what he loves doing, you may customise your gift to that passion. You may find at a Catholic book store a new book about Catholic education that a teacher would love. There may be items that are helpful for someone going on missionary activities.
Take a gift you would give to any other person, but customise it. While most teens would love an iPod and know exactly what to do with it and where to get the music they like, a priest may not be so current with technology. Also, the type of music a priest would like is much more difficult to find than Top-40 pop music. If the priest does missionary activity in a country without easy access to computers and Internet, it may be hard for him to download songs. Consider buying an iPod, purchasing traditional Catholic chants and music and downloading the music for him so you would give him an already set-up iPod so that all he has to do is turn it on. While some priests may be very technically talented, customising an item shows that you took the time not just to go to the store and buy something, but that you really thought about the person and made the gift personal. You can purchase a computer as a gift and purchase software for priests. There are programs that help organise church activities and budgets that would help schedule hospital and counselling visits or help the priest in whatever daily tasks he performs. Installing these programs for him and even going through them with him would be very meaningful and practical.
Since a priest has made a decision to limit personal items and dedicate their lives to the church, a meaningful gift may mean making a gift to the church. Many churches have cards that are sent as gifts after you make a donation to the church in a person's name. A church may be in need of a ritual item, maintenance or some practical item like chairs, tables or carpets. Donating such items shows the priest that you not only care about him, but that you care about the things he cares about.