Is praying for someone(even when it's not requested for you to do so) a "gift"?

I don't consider it a gift and if you chose to pray for me I don't see how i would be required to say thank you though that seems a little mean but in my opinion I didn't ask for you to and it's not going to mean it changes the situation that you prayed for and even if it does it is circumstantial

It depends. If someone offers me their sincere prayers, I do view them as a gift, a gift of their time, their good thoughts and their concern for me and I appreciate them immensely. If the prayers are offered as away to reproach (you know, the good old "I'll pray for you" some people throw around when they don't like what you believe) then no, it's not a gift, because it's not out of love and concern, but just to satisfy their own egos. I don't appreciate them in the same way, but I couldn't care less if they pray or not for me.
Personally, I only offer prayers when asked or when they're for a person I know would appreciate it if he/she knew.

We should make "DUA" prayer not only for ourselves but also for our parents, brothers and sisters, spouses and children, relatives and friends, teachers and other benefactors, destitute and struggling people everywhere. Our dear prophet Hazrat MOHAMMAD (May peace be upon him) said, The (Dua) prayer of a Muslim for his brother in his absence is readily accepted. An angel is appointed to his side. Whenever he makes a beneficial prayer for his brother, the appointed angel says, Ameen. And you may also be blessed with the same.

I wouldn't consider it a gift.  Prayer is for the pray-er.  I would appreciate the thought, as much as I appreciate kind thoughts and well-wishes from those who love and care about me . . . but I wouldn't fall all over myself in gratitude if someone said they were praying for me.  The belief in prayer is very contradictory.  People believe in the power of it, but will also have a number of excuses ready for when their prayers aren't answered - that god DID answer the prayer, just not how they expected, for example, or that god has other plans, or that prayer isn't meant to be used as a wish-granting device.  Regardless, it seems that if there is a god who's omniscient and omnipotent, then that god already knows what will happen (that's part of being omniscient, after all) and has determined it (part of omnipotent), so prayer seems a futile exercise, at best.

Is it a gift? No. An act of kindness? Maybe. But even then, I find it to be a bit presumptuous to think the person receiving the prayer will be grateful. It could, in some religions, be seen as very disrespectful.

I understand that some people do genuinely, deeply believe that prayer does good. Some of my friends believe this - I know these women very well, and I know that when they say "I'll pray for you" it's not a "I want to look like a good person without actually doing anything" trick. They really do believe that their prayer will help me (or whoever) and they choose to tell me of their prayer because they hope it will give me hope or make me feel better (even though they know I don't believe.. they hope it will help). So I do say "thank you" - it's a kindness that deserves my kindness in return.

But is this kind of prayer a "gift"? Well yes, but only in the same way that a warm hug when you are sad can be a gift.

Ahh, I miss the question a little. I'm not sure it's a gift so much. Perhaps in a way, if you know that your words brought them peace or comfort. But especially if they don't even know about it, no, I wouldn't really say...