Can instant coffee and fresh ground coffee be used for b'samim (spices) during Havdalah?
Good question! Short answer: yes, but probably only freshly-ground beans.
Mishna Brurah 216.16 writes, concerning the blessings on spices anytime you smell them during the week:
כתבו האחרונים המריח בקאוו"י כתושה והיא חמה שריחה נודף ואדם נהנה מאותו ריח צריך לברך ברכת אשר נתן וכו':
The late authorities wrote that one who smells ground coffee, if it is warm so its smell is strong, and one enjoys that smell, he must recite the blessing of Who gave fragrance to fruit.
Certainly if freshly ground, that's warm so its smell is strong; I'm not sure that would apply to a jar of instant coffee that's been sitting on your shelf for a year. (Unless he simply means this doesn't apply if the coffee is in the freezer -- or you live someplace where the room temperature is 40 degrees Fahrenheit?)
Flip back a page in the Mishna Brurah and you'll see that on fragrant fruits, Sephardim say the bracha in the present tense: hanoten re'ach tov bapeirot ("bless you God our Almighty sovereign of the Universe, who gives fruits their fragrance"), while Ashkenazim say it in the past tense: asher natan re'ach tov bapeirot ("who gave fruits their fragrance").
Okay, so that covers if I smell coffee on a Tuesday morning. How about for Havdalah?
Let's hop over to the laws of Havdalah. Sephardic practice is to make whichever blessing is suitable to this particular spice; Ashkenazic practice is to say the all-purpose "borei minei besamim" on anything, to avoid confusing people. The Mishna Brurah recommends as an extra stringency to therefore purposely pick something whose weekday blessing is always "minei besamim."
Conclusion: That would leave Ashkenazim with a very slight preference to use cloves, musk, or potpourri rather than coffee, but it would still certainly be acceptable, and its bracha during Havdalah would be the usual borei minei besamim. A Sephardic Jew using coffee for Havdalah would recite hanotein rei'ach tov bapeirot.