NETTUTS.com: 9 Confusing Naming Conventions for Beginners
Especially when first getting started with various web development languages, it can prove to be a difficult task to learn all of the various naming conventions from language to language. This can be even more confusing when developers disagree on what's considered best practice. To help ease the transition for beginners, this list will describe some of the more common conventions.
Some of the conventions that they mention that are more specific to PHP developers are underscores before property names, uppercase constants, capitalized first letters in variables and alternative syntax (like ternary).