I downloaded Zend and like many of the features, but the syntax highlighting allows for very little customization.

Notepad++ handles syntax highlighting much better but I don't like that the file browser is in a seperate window (instead of integrated with the IDE). I do like that variables in quotes are emboldened.

What other IDEs allow advanced syntax highlighting & customization?

I really hope to find a replacement for what I've coded on for 5+ years (homesite 4.0). See the attached screenshot for what I mean - HS tokenized the $ beside each variable, so it could be a different color than the variable name itself.