Basically, any creature with the words "when ~this~ comes into play, yaddayaddayadda" is a 187 creature. Uktabi Orangutan, the new Battlemagi, a lot of Kicker creatures, etc, are all 187s. Where the term "187" came from, I don't think we ever found proof of. I always assumed there were 187 of the things when the term was dubbed, but I'm probably wrong.
These abilities are often referred to as CIP effects (Comes Into Play effects), and are generally very powerful, since they net you a creature as well as a useful ability (with the exception of the occassional CIP effect that's a drawback, like "Sacrifice a creature").