Sometimes, in certain combinations of tones or words, the tones change. Where can I find a complete list of all tone changes that occur in Mandarin?
Complete rule of tones change is not a simple subject which can be understood just b a list. But there is a simple one I think might be suitable for you. http://www.trinity.edu/sfield/chin1501/ToneChange.html
Plus, if you are a foreigner who want learn Chinese without academic purpose, I think it's enough since many Chinese cannot use tones change complete correctly.
Here is a nice short overview on Mandarin tone sandhis: http://web.mit.edu/jinzhang/www/pinyin/tones/index.html If you want to read into the details I have found the following a very good source (from the father of another romanization): "Yuen Ren Chao: A Grammar of Spoken Chinese. University of California Press, Berkeley, 1968, ISBN 0-520-00219-9."
As xiecheng mentioned, tones changes are very complicated, and there is unfortunately little material on subject. Not that you care to this extent, but one can actually "map" tones using audacity (http://audacity.sourceforge.net). If you do that, you'll see that tones change a lot when they are in sentences and that how and the extent to which a tone can change, depends on where it appears in a sentence. For example, third tones tend to drop, but they rarely come back up when they are at the end of sentences. Also fourth tones change when they are next to each other, etc. These changes are not the same as the ones that occur when you have "不" or "一" right before a fourth tone, but I think they are interesting to study and knowing about them will certainly make you sound more "native-like."