If you're tight in space (e.g., for a conference abstract) and want all entries to read F. Author et al., BibTeX doesn't usually help you much (biblatex would allow that but the more common natbib doesn't). The easiest fix is to hack the .bst file!
bst files are terrible to read (they're made with makebst). Since typically you already have a bst you like and only needs to restrict the number of authors, the fastest trick is to crack it open and change the parameter 'numnames' to the value you want. For instance, in naturemag.bst, you replace the numnames #5 below:
nameptr #1
#1 + =
numnames #5
> and
{ "others" 't :=
#1 'namesleft := }
'skip$
to
numnames #1
You should do this in a local copy in the same directory as your TeX files.
Changing #5 for somethign bigger, e.g., #500, allows to display all authors.