I used to use
TextPad
Which does a nice job of syntax highlighting. It has tons of syntaxes available too, you can download them right of their website.
The product hasn't been updated in a while though so they may not work on it anymore, but from my experience its pretty good as it is.
Another you might want to check out is
UltraEdit
EDIT: a new version of textpad was released a couple of months ago, so apparently its still in development. I haven't used it in a while though, so I misjudged its active development.