When I ask someone to take a glance at something, I use:
jeter un coup d'œil
In the following phrase, do I still say "un coup d'œil" or do I use "des coups d'œil(s)"?
C'est peut-être une bonne idée de demander à Rod, Jane et Freddy de jeter un coup d'œil.
Since you assume that everyone will only take once glance, there is no reason to use the plural form, so the following is correct:
Ils vont y jeter un coup d'œil.
That said, the plural form of "coup d'œil" is "coups d'œil" (just because you give more glances doesn't mean you use more eyes), but I don't see any valid context to use it as illustrated in Gilles' example in the comments.
Like Joubarc said, there is no need for a plural. Even in this context:
Il faudrait régulièrement jeter un coup d'œil ...
or
Il va jeter un coup d'œil régulier à ...
Remark: the plural form of œil is yeux.
