Edit: upon further investigation, it looks like Etymotic was the original patent holder. That's what I get for trusting stuff I read on reddit. That said, Etymotic's designs are widely copied and/or licensed. (I'd guess Elacin is a licensee, since they use the same model numbers.)
Original: Etymotic is re-selling an ear plugs from a European company, Elacin. The same plugs get sold by a bunch of different vendors stateside, but the ER20xs at $15 on Amazon is nearly impossible to beat for price.
Some other plugs (possibly with a lower actual NRR, it's tricky comparing them when they don't use a standard test) sound better. The real question is what tips are most comfortable; I can't use triple-flange for long without feeling them dig into my ear canals, so I like the Loop or Eargasm Slide plugs with foam tips. (Eargasm also offers adjustable attenuation, which is cool.)