Aperture (iPhoto) quick view
Some options:


Make a Media Browser with Automator - takes about 30 seconds - and you can invoke it in many ways - including with a contextual menu its,
Install an app like http://www.karelia.com/imedia/ which will do the same with some extra bells and whistles.


That said, if you use an app like Aperture or iPhoto to manage your photos then they are the "go-to" apps for anything to do with your photos - including viewing them. What you have there is an argument for getting more Ram ;)

If you really want to you could run either app in Referenced Mode. This would leave your Masters (and note: Masters only) accessible via the Finder. While I am happy recommending Aperture in Referenced Mode, I would have significant reservations about running iPhoto in that way.