I like to look for sacred in the secular. Lenny Kravitz' "Baptized" is shockingly reverant. Though it doesn't name Jesus or God overtly, the subtext of the lyrics is a very clearly Christian meditation on baptism.
I also think that "Timshel" by Mumford and Sons is about baptism, with images of water, death, birth, and communal support. Not sure how many congregations would see it that way, though.
Thank You for Saving Me is popular for baptisms round here, though I'm not a big fan.
Doerksen's The River is a good one.
You're right. There aren't enough.
We used to sing "I am a new creation" during baptisms, just after they'd re-surface.