You might find the test first user interfaces list of interest.

Sure, I have test suites for the non-GUI components, but sometimes, as it is in my case, the GUI itself is the bulk of the functionality

Being able to get at functionality via the GUI is often a sign that there is too much application logic is sitting in the (in MVC terms) the view/controller layers.

Can you move more application logic out of the GUI layer to make things easier to test?

Some possibilities (like print-screening and comparing images) sound just outright scary.

One interesting technique I've seen is to take automatically generate snapshots of all the screens in an application and wrap them all up in a little animated GIF, showing a couple of screen shots a second.

Automatically generated at integration time the little animation was always playing on a machine in the corner. Took less then a minute to look at quick overview of the whole application and spot any major foul ups in the look, if not the feel.