Matthew 22:30 speaks of people after the resurrection not participating in marriage–they become "like the angels." However, this does not mean people are genderless. The masculine, not neuter, pronoun is used many times to describe angels (and HE was like...HIS appearance was like, etc.). So there is no real indication that the angels are genderless beings.
There is nothing in the Bible that indicates people will lose or change their gender in heaven. In the book of Revelation (chapters 21-22), it seems that God is making things not just like they were in the Garden of Eden, but even better. Remember that gender is not bad--it is actually a good thing. God created Eve because Adam needed someone to complement him. Marriage (impossible without different genders), the model relationship between a man and a woman, is a picture of Christ and the church. The church is the bride and Christ is the groom (Ephesians 5:25-32).
Although it is not explicitly taught in the Bible, it seems most likely that people retain their gender after death. Our genders are a part of who we are. Gender is more than physical–it is part of our very nature and part of the way we relate to God. Therefore, it seems that gender will be perfected and glorified in eternity. It is also noteworthy that Jesus retained His gender after His death and resurrection.