Geeqie runs great on Xfce without pulling in bunches of de dependencies. Like Sproggy says, Thunar can show thumbnails. I'm OK with some Gnome apps and applets in Xfce so long as they don't pull in bunches of Gnome dependencies, wouldn't even think of installing 'anything KDE' over my Xfce 4.8 install. If you have KDE as your main base install with task-xfce to log on from KDM that's fine but 4.8 isn't even available as a task.