The best teaching I have ever heard on identifying and releasing the gifts comes from Harold Eberle, who clearly identifies three separate categories of gifts in Scripture - the motivational gifts which operate on the natural level and are attributed to God the Father, the gifts of the Spirit which are supernatural abilities and not natural talents, and the five-fold ministry gifts of the Son.   You can order a copy of Harold's teaching here.

Here are links to three free on-line inventories of ministry gifts.  Free on-line spiritual gift inventories usually enable you to print but not save.  These three, like most of the ones I found, seem to combine the three categories of gifts; I haven't yet found a free online inventory of gifts that clearly distinguishes between these three categories of gifts.  As long as you keep those limitations in mind, they can be useful tools.  Have fun!

Spiritual Gifts Inventory - BuildingChurch.net

Online Spiritual Gifts Test Inventory - Ministry Tools for Believers

Team Ministry Spiritual Gifts Inventory - Church Growth Institute

Understanding and Releasing the Gifts - Teaching notes from the seminar held at City Church on Feb 21, 2009.  
NOTE : Some of the material in this seminar was based on concepts in a seminar originally given by Harold Eberle.