I'm going to be blogging about spiritual gifts in preparation for a teaching series on this subject. I'll start with a working definition. This definition is fresh in that I made it up after doing my research, but it is subject to further insight.
A special ability, proficiency, or status that God providentially grants to particular individuals by the Spirit for the purpose of continuing Jesus' work of drawing unbelievers and building up believers.
By 'special ability' I refer to gifts largely disconnected from the person's previous experience. By 'proficiency' I mean the heightening or sanctification of a previously existing God-given talent. By 'status' I am including certain offices, institutions, and states of existence that are gifts of God to the church.
God gives these gifts providentially, by His wise choice, to particular people (not to everyone). Of course, the main recipients are Christians. That being said, there may be circumstances where a non-Christian individual is given a spiritual gift for a specific purpose.
The purpose of spiritual gifts is to continue the work of Jesus Christ. The church is the body of Christ on earth. Nearly all of the gifts were demonstrated in his 3+ years of ministry. There are 3 main ways that God uses spiritual gifts: 1) As a sign to unbelievers to confirm His presence 2) As a means to growing the body of Christ in maturity and 3) as a way of meeting basic human needs.
I think that this definition is broad enough to account for the biblical material and yet concise enough to be useful for discussion.