Does it amount to plagiarism by supervisor? I have been working on an idea for last 2 years almost independently along with other research works. My advisor did not believe in my work much initilally, so I did not get an RA for two years even after requesting. Recently, I am getting encouraging results with some specific examples and scenarios with good hope for success to solve a complex problem using that idea. I have not published the work yet. Initially, my advisor was not interested in the idea partly because the work is not his area of expertise and insisted that I spend my time in other research projects with a senior colleague. I pursued it with my interest in spite of RA support, but with new results and potential benefits of the approach my advisor became extremely interested and even described the work as the next big idea in our lab meetings. I am happy about it or maybe he says it to make me happy.
However, recently I encountered a situation which was difficult for me to comprehend. I found my advisor present a perspective paper along with many other renowned experts in the field, proposing and highlighting the approach I have been working on as the future direction and visionary in the field along with other important developments in a conference. Even though I was not a co-author in that paper and my work was not cited or even acknowledged, I consoled myself as my advisor was alluding me that he was promoting the idea; it was an advertisement of the work (of course with out any acknowledgement). 

As he was not the first author of the perspective paper and there is a possibility that first/other authors can make claim of it, he asked me to file an updated technical report in the department before the  paper is published. It looked to me like he wanted to promote himself among his colleagues with that idea with out acknowledging it to me before the audience and greater scientific public where it matters. 

I happened to attend the conference as a PhD student, and found that the presenter of the perspective paper (whom I don't know) presented more than half of his talk on my idea with my slides that I shared with my advisor, and there was no acknowledgement or mention of my report or work. It was even worse to see that some of the terminology that I planed to use, was disclosed and few misinterpreted while explaining.  

Even then, people really seemed to liked the idea and the approach and many are convinced that the idea is going to impact the field. While I saw a very drastic change in the way my advisor treated me recently, but what really made me sad was when my advisor asked me to refer to this perspective paper (to which I was not a co-author) in my impending submission (on the idea).  

I feel like it was unfair but I don't know if research is done this way in academia or if it is perfectly legit to do something like that. I decided not to cite the perspective paper with possible consequences. I just wanted to know how other students handle such situations effectively and if such a thing is a common practice.

Edit: I do have all email traces and even a previous publication explaining part of the idea and a recent technical report submitted to the department with the complete idea.

UPDATES 

June 2014: 
I have continued with the situation I described above honestly because as a student I hardly have any options and as suggested by many that it would be an academic suicide. But, it had impacted me severely, mostly because I believe that any good idea I will bring to the table will be stolen or misrepresented and there will be cleaver manipulations to take ownership of them. I will take two steps forward and three steps backward. I could hardly perform in my potential. I will let you know my ordeal soon and many thanks for your kind help and support.
As far as I understand the situation, it seems to me that your advisors' behavior is borderline, even if likely on the wrong side of the border. Since it does not look like a very clear and frank misbehavior, even if you are perfectly right it would be tremendously difficult to prove it beyond doubt. In case of doubt, you could end up being seen more as the trouble maker than as the one who came up with that great idea; the surrounding people to whom you could complain (department head, etc.) would hesitate a lot to go against tenured faculty when the misbehavior is not crystal clear, etc.

With this in mind, I would strongly advise you not to confront to wildly with your advisors. You can (and should, as advised by Shion) discuss with them the fact that you are uncomfortable with the way they presented things, with the use without permission of your slides, and so on; but always let them a way to discuss it calmly. If they feel cornered, there will be little chance of the situation not degenerating into a conflict, and it would be very difficult for you to survive professionally a conflict with your advisors.

You could cite their perspective paper in a way that friendly makes explicit that the idea is yours. Your aim should be to get decent credit for your idea, even at the cost of letting your advisors benefit from it: think about what you have to gain or loose first, rather than about what they have to unduly gain or what you can cost them.

If everything goes smoothly, you can get into a good position to build on your idea, and be on track for your career. 
Once you're a respected tenured faculty, you should remember this episode and be supportive of young researchers.