French has that rule that whenever a masculine entity is part of a group, the whole NP will default to masculine as far as agreement goes. My native language, German, also defaults gender to masculine, whose forms are usually the least marked, though plural may also be analyzed as a separate, fourth gender. However, I wonder how common defaulting mixed-gender groups to masculine is crosslinguistically (especially outside of Standard-Average-European) if there's also e.g. a neuter category.
See Corbett's contribution to Shopen et al. ed. Language Typology and Semantic Description (2nd ed.), esp pp.268--73, where he discusses default genders.
Oneida has three genders (Masculine, Feminine, Zoic) in the singular, but only two (Zoic, Masculine) in the plural (groups of all females are marked as Zoic). Mixed groups default to Masculine (Lounsbury: 1953:52).
Hebrew (and, I guess, Semitic languages in general) defaults to masculine too for a mixed group. But it doesn't have neutral.
Hebrew has four genders: male, female, male plural, female plural. For the plural form, if there is so much as a single male in a group of people, then the group is addressed as male. A hairsplitting example would be in literature aimed at women: despite the fact that a man could read such a magazine, the audience is in fact referred to in the plural female gender.