dude: the OED has citations for the old male-only form of dude dating back to 1918 (!); its earliest citation for a gender-neutral dude is a 1974 description of campus slang at the University of North Carolina at Chapel Hill. (A later one is the 1995 comedy film Clueless.)
This can get awkward because dude is in fact quite frequently used (in nominative form) to refer specifically to males.
man: the gender neutrality of the usual noun man/Man can be possibly disputed, but in this case I mean the vocative form. OED’s entries (IV) 16 (a) and (b), specifically. 16a: Used to address a person (usually a man, but sometimes a woman or child) emphatically to indicate contempt, impatience, exhortation, etc. 16b: […] Also […] among African-Americans. Used to address a person (in many varieties of English, irrespective of sex) parenthetically without emphasis to indicate familiarity, amicability, or equality between the speaker and the person addressed. Now sometimes with loss of vocative force.
you guys: the standard third person plural vocative form of address (completely irrespective of the gender makeup of the group) in several English dialects, including that of the Bay Area (although some at UC Berkeley seem to insist on the foreign y’all, perhaps due to the perceived unfairness of referring to a mixed-gender group with guys). Whether guys itself can be gender-neutral is debatable; it can certainly be used in ways that are unambiguously male only (“guys and girls“). There is also the spurious debate as to whether it should be gender neutral, a debate that, for example, he has roundly lost. (The OED has excellent coverage of this.)
Singular guy I think it is safe to call strictly male only.
girl: (in the vocative; occasionally written gurl, or even qurl; see the Cognoīntellectualist’s Dictionary) OK I’m sort of joking about this one. I once heard it used by a girl talking to a guy (in place of the more standard “Dude… ” or the more vulgar “Bitch…“). She realized it was an unacceptable* usage, apologized, and continued using it anyway. Perhaps it will catch on.
*in the grammatical sense, not in any moral sense
fanboy: Unfortunately in this instance the OED, American Heritage Dictionary, and Merriam Webster all have this one wrong, as they all specifically limit fanboy to males, perhaps in a mistaken belief that a female fanboy must be referred to as a fangirl, a word which also appears in all three (and is not gender-neutral).
Urban Dictionary, interestingly, does have this one correct*, as none of the entries for fanboy mention any restriction to males. (Then again, “there are no girls on the internet”1.) Fangirl is explicitly limited to females.
*This situation is surprisingly common for recent-ish colloquial usages.
My only actual citation for this is the short self-bio given by Michele Titolo in reddit’s announcement of her hiring (along with several others), where she describes herself as “reddit’s new Certified Apple Fanboy™…er iOS Software Engineer“. (As a sidenote, I had to look her up to ensure that she was actually female, as Wikipedia warns that Michele is a male given name in Italian. Although I suppose the mention of /r/TrollXChromosomes was a giveaway.)
There are undoubtedly many more.