good image viewer for mac working without importing?

after one year with my mac i'm still looking for a photo looking and managing tool that works without importing based on my own folder structure. and beeing able to display photos in fullscreen mode. something like ACDSee for windows.

iPhoto is working with importing and shows the pics in its own arrangement. my own system gets lost.

at the moment i use expression media. it needs importing but keeps my own structure and works like the finder (and changes also have affect in the finder). unfortunatelly expression media is very slow and misses some features.

any experience with other software?
regards
thomas

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