Nothing. No difference. $ is a valid character in a JavaScript identifier but has no special meaning. In fact, in the ECMAScript 3 specification in section 7.6 it states that
The dollar sign ($) and the underscore
(_) are permitted anywhere in an
identifier. The dollar sign is
intended for use only in mechanically
generated code.
... although events have now probably rendered that recommendation obsolete. Indeed, the recent ECMAScript 5 spec omits the final sentence.
