Does anybody know of any online resources (or maybe even books) that go over the "beginnings" to driving ultrasonic transducers, as well as how to receive an ultrasonic echo, and pick it out (for rangefinding)?

I found one article online...but it glosses over it almost too much.
http://www.ee.latrobe.edu.au/~djc/Ul...ltrasonics.htm

 

http://www.picbasic.org/articles/ult...periments.html

http://www.interq.or.jp/japan/se-inoue/e_pic6_6.htm

http://www.web-ee.com/Schematics/Mot...onDetector.pdf

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A lot of these documents just attach the transmitter directly to the pins of a PIC. What is all the other stuff I sometimes see then about matching transformers, and push-pull drivers, etc? They're just for higher power transmitters?

I'm also a bit curious about what it would take (and if it would make much difference) using a sinusoid to drive the transmitter rather than a square wave.

 

I think the output of an ultrasonic transducer is sinusiod even if you drive it with an square pulse

don't know what are you doing but I am not sure if you could use ultrasonic sensors with high power due to their fragile piezo.
I managed to drive few of my ultrasonic transducers(16mm) with a bridged amplifier at 17V power supply, they are ok with 34V yet.
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http://coecsl.ece.uiuc.edu/ge423/spr...ltrasonic.html

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Yes, for maximum range you need more power - and this requires more voltage across them.

It's a resonant device, it will output a sinewave anyway - as 'epilot' said.

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