Yours is an intriguing question - and a very political one as well.
The word "revenge" triggers a knee-jerk reaction in many people, somewhat similar to "Nazi" or "conspiracy theory." Many people swear revenge can never be good and that merely harboring hate negatively impacts your mental and even physical health. In fact, some of the warnings of the consequences of revenge are a little loony, similar to much of the tripe written about conspiracy theory.
A big reason for this is likely the evolution of the state. When our ancestors began to congregate in ever larger tribes, cities and nations, they had to modify their behavior. Disputes were increasingly resolved by the state, and vigilantism was increasingly vilified.
Of course, there is an enormous danger in letting a major city or country lapse into feuds and personal vendettas, especially when some of the individuals harboring thoughts of revenge may be a little unhinged.
But what if the state itself is the enemy? If another country bombs your country for no just cause, killing your family, is it unethical to seek revenge? What if your government supports a rich tyrant or corrupt operative who spits in your face again and again?
The ethical ramifications of revenge in such situations may be very different from hiring someone to assault a person who merely insulted you.
However, the answer to your question is all over the map. I've asked similar questions and have learned that the broad consensus is that revenge is evil, period. However, not everyone (including myself) is in agreement.
I just read Forgiveness: A Philosophical Discussion by Charles Griswold. It was very interesting and has some good points, yet it also smacks of propaganda. I think the author completely missed the boat when discussing forgiveness in the political arena.
Anyway, here are some things to think about when pondering the ethical ramifications of revenge:
Have you sat down and carefully analyzed the situation and/or sought help through official channels before resorting to revenge?
Does the magnitude of the crime committed against you merit revenge?
Are you responding to a single hurt, or has an individual or organization repeatedly hurt you? There are situations where you may have just two options: Either submit to continuing exploitation or hurt, or take the law into your own hands. I've experienced this countless times.
Are you the only victim, or are there others? I've written some pretty nasty, vengeful (but truthful) things about public schools officials who have hurt me. This could be regarded as selfish or spiteful. However, these same people have hurt many other teachers, not to mention children. If I hurt a school official who hurt me, and that individual was also a pedophile, I would be even more proud of my action.
Ultimately, the ethical ramifications of revenge are a reflection of your personal moral code. However, if you even entertain thoughts of revenge, you might want to be careful about sharing them publicly, because most people will condemn you.