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 The paper will not be published until 2013 (if at all).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.
Yes, this is very common. Indeed, theses are often verbatim copies of one or more published or submitted papers.
I would say you should cite the conference paper, listing it as "Submitted". You should also check with your university's thesis guidelines. It is very likely they will tell you how to cite work that is/will be published elsewhere.
While reusing material is typically done there are three concerns.
The first is citation. If it is in press or published at the time you submit the thesis, I would cite it. I wouldn't bother citing manuscripts that are in preparation/under review/in revision.
The second issue is copyright. Many journals and some universities require you to give up copyright control. Most make concessions, especially for articles, less so for book projects. You need to check and read the rules.
The third is being scoop. Putting your stuff in the public domain is important, but it also puts you are risk. Someone might independently build on your research publish your second chapter before you or conduct follow up research which reveals a huge hole in your research.
While many universities accept sandwitch theses, the only thing that can give you the right answer are the examination regulations you're subject to.
There are cases when parts of thesis work are not allowed to be published (in an article) though that can also create difficulties with the regulations.
Usually the university will want to get a paper out of the work in addition to the thesis. So the content being published is usually seen positive.
However, they may still not accept verbatim copy of large parts of the text but expect you to rewrite it so that your thesis is one "unbroken" piece of text written by you yourself.