Click here to read an interesting piece on "Instrumental Music in New Testament Worship".
Read and then come back here to write your thoughts in our comments section.
BTW, much of the material online advocating a cappella singing is either Baptist or Church of Christ. I've seen some Reformed stuff also. Last night I ran across an article from a Mennonite point of view -- A Cappella Singing, by Leland M. Haines -- so am linking it for those who might be interested. [Note: this is not the position of all Mennonites.]