I believe the St. Valentine of St. Valentine’s Day is no longer officially recognized. I had details in a book but I left that book at home while at school this year. A search at Catholic.org’s Saints & Angels page shows a number of St. Valentine’s but none of which are the right one.
My personal patron saint is St. Benedict. At first the choice was merely pragmatic; I am studying Forensic Toxicology and he is the patron of proof against poisoning. However, the more I explore his life and his Holy Rule for monastic life, the more I have come to appreciate what he did for the church and his wisdom for living a holy life (whether monastic or not). For the most part, I have reached certain conclusions and then found them espoused so much more elegantly and completely in his writings and life.