I would recommend e – text editor from http://www.e-texteditor.com/ which supports TextMate bundles such as the Liquid bundle. I’m using the Liquid bundle in TM on my Mac and it’s indispensible. e is an awesome product, and well worth the price.
i use notepad++ too, which i find excellent. so far, i haven’t had highlighting for liquid, which is a little off-putting, but thanks to your question, i just realized you can customize your syntax highlighting – check out “user-defined syntax highlighting”.