In this week's parsha, Naso, Aaron and his sons learn how to bless the children of Israel:
May the LORD bless you and protect you.
May the LORD deal kindly and graciously with you.
May the LORD bestow His favor upon you and grant you peace.
This blessing has been incorporated into the blessings given to children by their parents on Shabbat. I think it's a beautiful and hopeful prayer, especially when directed at children.
In traditional communities, the kohanim (the descendants of Aaron and the priestly class) still recite the priestly blessing during certain parts of Shabbat and holiday services. When doing so, they use a hand gesture that may seem familiar to you. And yes, Leonard Nimoy knew exactly where the gesture originated when he first suggested it on the set of Star Trek! Click here for a lovely description of the synagogue ritual from Spock himself.