What is a camera app for the iPod touch geared towards filming video?
When I need more control over the video I'm recording I use Canopy Camera Tools. The Canopy app lets you choose a separate focus and exposure point - unlike the stock Camera app. It also lets you lock the white balance once you found a good exposure. Those features are also available when you want to take a picture.
You can also make time-lapse video's with Canopy.

I'm sure there are alternatives to Canopy but this is the app I use.
There are also apps that - unlike the stock Camera app - let you zoom while you're recording a video but since any zooming is achieved through digital zoom and not optical zoom they will degrade the quality of the video.