You can use the bibliography management tool JabRef (starting with version 2.10). Use the setting Preferences⇒File⇒Field saving options⇒Start field contents in same column. Just opening and saving the file will align the equals signs.
Before:

After:

I’m not sure, however, what determines the number of spaces before the equals sign. Also, as you can see, JabRef sorts the fields according to what it deems obligatory and optional fields, and secondly alphabetically. I’m not entirely content with that functionality, but then again, if you’re using JabRef, you won’t be fiddling with the raw bib files too much anymore at any rate since you have the comfortable front-end for editing your bibliography file, as you remarked yourself in your answer about BibDesk.
.bib
files to keep things more-or-less aligned. I don't think there's any particular trick here unless you editor can impose that sort of order for you ;).M-x align-regexp
then=
and return ...bibtool
a utility tool designed to modify.bib
files, it seems to offer quite some options to align the keys, see §A.5. Parsing and Pretty Printing, pp. 24-28, esp. pp. 25 sq. of the manual. There also isbibclean
(--align-equals
is probably what you are looking for).