I've come across DOZENS of attempts to categorize the spiritual gifts. I don't think categorizing them is very important, but it may be helpful for those hoping to better understand them. It could also be somewhat harmful, if we fail to recognize that our categories are extra-biblical and imperfect. So keep in mind that what you're about to read is just my attempt to be helpful. I do not insist upon these categories dogmatically.
I believe that some of the spiritual gifts are PRIMARILY intended as signs pointing toward the authority of Jesus and His movement. Sign gifts witness to unbelievers, perhaps especially those who are religious seekers. They tend to be on the more sensational side insofar as they are intended to get the attention of people so that they open themselves up to the Gospel.
Some of the spiritual gifts mentioned in Scripture (and seemingly many of those not mentioned in Scripture), may be classified as serving gifts. Since loving sacrifice is central to Christianity, it is not surprising that service gifts make up a category among the spiritual gifts. Serving gifts often look like applications of the fruit of the Spirit. Those with these gifts often work behind the scenes.
A third category of gifting has to do with speaking. It is not that those given spiritual words to share are not servants that necessitates a third category, it is that revelation from God is integral to the church being and doing what it is called to be and do. We need a word from God and those who have been given speaking gifts bring those words to us effectively.