There are many different styles of variable names that I've come across over the years.
The current wikipedia entry on naming conventions is fairly light...
I'd love to see a concise catalog of variable naming-conventions, identifying it by a name/description, and some examples.
If a convention is particularly favored by a certain platform community, that would be worth noting, too.
I'm turning this into a community wiki, so please create an answer for each convention, and edit as needed.
The best naming convention set that I've seen is in the book "Code Complete" Steve McConnell has a great section in there about naming conventions and lots of examples. His examples run through a number of "best practices" for different languages, but ultimately leave it up to the developer, dev manager, or architect to decide the specific action.