Why is a Sholom Zochor called a Sholom Zochor?
This page cites a couple of other reasons:
The second word means "remembering" (as in זכור ושמור), because the child will have to start "remembering" the Torah he previously learned in the womb and has now forgotten. (R' Yaakov Emden)
Also with the meaning "remembering": it's that he should recall the oath he took at birth (Niddah 30b) to "be a tzaddik and not be a rasha." We associate this with Shabbos, the first mitzvah that he experiences. (Also R' Yaakov Emden)
It means "peace" and "male," in keeping with the Gemara's statement (Niddah 31b) that כיון שבא זכר לעולם בא שלום לעולם. (Noheg Katzon Yosef)
Taame Haminhagim 903 starts off by saying he's going to explain why it's called a shalom zachar and proceeds to cite Tosafos (Bava Kama 80:1 s.v. "L've") as saying that the reason the g'mara there calls a shalom zachar a "salvation of the son" is that he was saved from the womb (citing "וְהִמְלִיטָה זָכָר", from the haftara of Shabas rosh chodesh, related to words meaning "escape"), but then doesn't, as far as I can tell, complete the thought about why it's then called shalom zachar, instead giving what is, as far as I can tell, a completely separate reason: that it's called shalom zachar because it takes place on Shabas which is called shalom. It seems very odd to me, so perhaps I'm reading it wrong, but that's what I'm seeing.