One way to look at the issue is to look at the broader category of fornication. The American Heritage Dictionary defines fornication as "Sexual intercourse between partners who are not married to each other." Premarital sex clearly falls in this category, so let's now look at what the Bible has to say about fornication.
Fornication is clearly condemned in the Bible, and is done so in a very succinct manner. First, Christ declares fornication evil as shown in Matthew 15:19 For from the heart come forth evil thoughts, murders, adulteries, fornications, thefts, false testimonies, blasphemies. Next, we are admonished to not commit fornication in Acts 15:20 But that we write unto them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood. Finally, the punishment for commiting fornication and not repenting or seeking forgivness is given to us in Galatians 5:19-21 Now the works of the flesh are plain: fornication, impurity, licentiousness, idolatry, sorcery, enmity, strife, jealousy, anger, selfishness, dissension, party spirit, envy, drunkeness, carousing, and the like. I warn you, as I warned you before, that those who do such things shall not inherit the kingdom of God.
In today's environment it is difficult to remember that fornication is a serious evil. We are bombarded with sexual messages in the movies, on TV, in books, in advertisements, and the list goes on. When someone you love wants to have sex it is hard to resist, I'll be the first to admit that, but we need to remember that temptation is no excuse. Adam was punished for falling into the temptation of Eve, who God made for Adam. Why shoud we expect to be treated any differently?