Creating a new module for Joomla 1.5 is easier than you think!  If you can do a little coding, you can create a module.

Do you want to display a flash object in a module, but the Custom HTML module parses out the code?  Do you want to insert some javascript on certain pages for statistics tracking?  You can put this code into your custom module.

Do you want to pull data from a component and display it in a module position, but there isn't a module that does this quite the way you need it?  You can build a custom module based on an existing module.