Question: What are the spiritual gifts God gives to believers through his Holy Spirit? How many of them are there? What ones are considered fruitful?
Answer: Beginning with your second question about fruitful spiritual gifts, there is one Scripture that gives us a general answer. In the book of Colossians Paul tells us we should live our lives worthy of our calling, "being fruitful in every good work" (Colossians 1:10). This has a connection to the subject of your first question that is broadly covered in many Scriptures.
The first and most important of all the spiritual gifts is actually available to all truly converted people. This precious present is GRACE (2Corinthians 9:14, see also Ephesians 2:8).
Because of conversion and grace, God uses the individuality of each person in order to impart gifts, skills, or aptitudes. They do not have to be great qualities, as humans would view them, but God sees them with the perspective of the Master Builder.
God's Spirit of grace should manifest in the believer the 'fruitful' abilities or what is called the "fruit of the Spirit" in the book of Galatians, chapter 5, verses 22 to 23. When you read these verses, you will notice that LOVE is first on the list. Love, then, is the greatest thing God can give and is the result of his work in a Christian. Without it, everything else is to no avail.
The fruits of God's Spirit, with love at the head of them all, are also labeled the "gift of righteousness" in Romans 5 verse 17.
Combining the gifts listed in 1Corinthians 12, Ephesians 4 and Romans 12 produces the following list of fruits generated by God's Holy Spirit within a person. A person can be blessed to organize projects and lead others, to teach and encourage others in the Bible, to discern spirits, to evangelize, to have extraordinary faith or generosity, or be able to heal others. They might be empowered to be specially dedicated to helping others (the ministry), to interpret or speak messages in different languages, to work miracles or to speak prophetically. Christians may receive power to be extra merciful with others, or the gifts to be knowledgeable and wise on particular topics.
No matter what spiritual gifts a Christian is given, it should always be remembered that God gives them so that they can be used to serve OTHERS. They should never be used to increase our own ego or to look better in the eyes of other people.