I like TextPad, which has a free syntax add-in that can be /configured/coordinated with QTP settings (such as Tab settings, syntax color, font, etc.). There are also many other free personality syntax add-ins that can be downloaded for free as well. See more info at www.TextPad.com. Note that you can download a free fully functional version, but to license the product you will need to now pay $32 US.
But, having just upgraded to QTP 9.2, I think I will just use the QTP editor, which I think is just fine for *.vbs files--especially now that QTP (finally!) supports a tabbed multiple document interface. I also could not be happier that you can now debug *.vbs libs in the QTP gui--those libs that are included via the Test-->Resource tab (lib debugging is not available if you include libs using the ExecuteFile() command--maybe that will come later).
One last plug (I have no connection with this company) for the TextPad folks: I see they now also sell a very interesting editor called WildEdit, which uses regular expressions to recursively prowl through a directory structure and edit (again, using regEx) multiple files. This could <u>very</u> useful for some of my/your global QTP changes that are occasionally needed across two or more tests (I know, all offending syntax/objects should have been encapsulated in a single action or lib function, but there are times...).