I’ve lost count of the amount of times I wanted to execute custom code in one of my modules. It’s not exactly hard but depending on template choice, what libraries are included and what I want to do I often have to jump through hoops trying out all the usual suspects or use something less than simple.
Advanced Module Manager and Jumi will do this for me or I could code my own module (not difficult by the way) but that seems like a bit of overkill unless I want to use their features or have time to do some coding. But there are a few simpler choices for when you require less of a bludgeon.
Blank module — probably the simplest one of all to use. Like the custom html module.
Custom HTML Advanced — just like the joomla custom html module but allows javascript and css.
TopDrawer — a Swiss Army Knife type extension. This one has alot of uses. Have css, javascript or php executed from a button click. Comes with built in gallery of button graphics.
Flexi Custom Code — easy to use. supports javascript, php, html and css.
Do note that depending on which you pick you may need to edit the filtering options in your Joomla backend and turn off filtering for super-users (1.6+). So if you want to have custom code in a Joomla module get downloading!