I am finishing writing my master's thesis (~100 pages) and I also just submitted a paper (8 pages) to a conference. Since both are on the same subject and I am an author on both, is it ok if I reuse one page from the paper and put it in my thesis without many changes? The paper will not be published until 2013 (if at all). Is it necessary to cite it in any way?
Yes. It is certainly okay. Indeed, general practice when writing a PhD thesis is to produce a number of publications that add up to the thesis, whether directly (using staples) or by a good deal of massage. Some published material may be omitted and some additional material may be included. There's no reason why this shouldn't apply to a Master's thesis, too.
It is a good idea to cite the paper in the thesis (if the paper has been accepted for publication) and the thesis in the paper, if possible.