Presbyterian perspective
I look at this issue from a slightly different angle than the Biblical agruments for or against the altar call presented in these posts. When growing up as a Presbyterian, (PCA), after a long, stoic, dry sermon, there would be a prayer and a choral response, and that was it. There was not even a mention of the message just preached, the Holy Spirit working in your life, or an invitation to see the pastor or deacon/elder after the service. It was almost like a mechanical assembly line.
I am the first to agree that the altar call has been abused as a sales tactic, that too many verses have been sung to draw a response, and maybe even given some the impression that walking up front is a part of salvation.
I also agree with Brother Jim that when the Holy Spirit convicts, we respond. All that saves us is faith in Jesus Christ. However, that all being said, when altar calls are conducted properly, I appreciate the forum at the end of each service as a way to express to the Lord that something is going on in my life, while my fellow believers and church members are there watching me. Contrast this with the picture above of a typical service such as I grew up in, and I am grateful that this is part of the worship service.