This plugin will highlight all occurrences of the php variable under cursor. This is help full both while writing and reading code. When writing, this helps to prevent typos, by highlighting the variable as long as the name matches, or not highlighting if there was a typo. When reading, it can improve readability by quickly showing the location where a variable is actually used.You can fully customize highlighting.
Screen shot http://i.imgur.com/f9N2asZ.gif