Looking for properly formatted BibTeX citations for articles or books can be tedious. I used to use the functionality from Google Scholar, but found that for many cases the BibTeX files are poorly formatted, are missing information, or even contain wrong information.
For mathematics papers, http://www.ams.org/mathscinet/ appears to be a reasonable alternative. But it is manually maintained and unfortunately a paid service (many universities have access).
Are there other similar databases, possibly for other fields of science?