<p>Alas, it varies wildly. You’d need to look for each and every individual program you apply for, <em>and</em> consider that against the cost of living in that community. </p>
<p>Something to bear in mind is that it’s like any other job market, affected by supply and demand. The number of highly qualified people that programs look for in their PhD candidates in each field determines how replaceable each one is, and thus how much they’re worth. Humanities fields generally have the lowest PhD stipends, intellectual sciences middle of the pack, and dork sciences (Comp, Chem, some branches of obscure engineering) the highest. With the exception of programs that will turn you into a person with high income potential (MDs being the most obvious example), they don’t offer a stipend except to extremely talented, competed-for students at all.</p>