There is a sense in which different sins are equal and a sense in which sins are not equal.
In the Sermon on the Mount (Matthew 5-7), Jesus indicates the way that all sins make us equally guilty before God. He was speaking to people who thought that they were innocent before God and better than other people because they were not guilty of "big" sins. We all minimize our sin because we think that we haven't done anything as bad as somebody else. We may not have murdered anyone or committed adultery, yet we have had sinful anger and lust in our hearts. Jesus tells us that even if we are only guilty of "little" sins, we are still fully guilty before God. As it says in James 2:10, "For whoever keeps the whole law but fails in one point has become accountable for all of it." So as far as our legal stance before God, any sin makes us fully guilty of his judgment. We don't become more guilty by committing more sins or by committing bigger sins; we are fully guilty already. Case closed.
But that does not mean that all sins are exactly the same with regards to how the sin affects us and our relationship to God and other people. For example, I would rather have you slap me in the face than shoot me in the head. Both are sin (and would make the offender guilty before God), but they affect me quite differently. And I would hope that God would view these two actions differently as well. We also see this difference in Scripture. When Jesus was testifying before Pontius Pilate, he referred to Judas, saying that "he who delivered me over to you has the greater sin" (John 19:11). Similarly, at several points in Ezekiel 8, God refers to "greater abominations." In Leviticus (4:2, 13, 22) God speaks of "unintentional sins." Unintentional sins are still sins, yet the punishments are less severe than for intentional sins. In the Old Testament law, different sins deserve different punishments because not all sins are equal. These examples indicate that although any little sin makes us legally guilty before God, different sins lead to different results. This is also seen in Jesus words in Matthew 5:19, where he speaks of "the least of these commandments," implying that not all of the commandments are of the same weight.
Further, the Bible speaks of differences in sin based upon who commits the sin. Romans 1:18-23, Romans 2:21-24, and Luke 12:48 reveal a connection between greater understanding and greater guilt. And James 3:1 also makes it clear that "we who teach will be judged with greater strictness."
So are all sins equal? In one sense, yes, but in another sense, no. The good news of the gospel is that Jesus' death on the cross is sufficient to fully pay the penalty for all of our sins--big sins, little sins, and everything in between.