If an inventor has been left out from a patent application, which has been filed, is there a deadline for including the inventor in the patent?

FOR U.S. ONLY - See USPTO AIA Blog, Mon., Jan 07, 2013.

For example: For a Non-provisional patent application, Adding or deleting inventor(s) requires:
•A request under 37 CFR 1.48(a) to correct or change the inventorship;
•A signed ADS including inventor information for all actual inventors as required by 37 CFR 1.76(b)(1); and
•An executed inventor’s oath/declaration under 37 CFR 1.63 for any added inventors (37 CFR 1.48(b)).
Note: For applications filed prior to 9/16/12, where a 37 CFR 1.48(a) request is filed after 9/16/12, the inventor’s oath/declaration must be compliant with the prior version of 37 CFR 1.63, including the requirement to identify the entire inventive entity. However, only the added inventor needs to execute the oath/declaration identifying the entire inventive entity.
FEE: $130 per 37 CFR 1.17(i)