People hate on the default blue Luna theme, but there was a perfectly professional Silver version, and the later (black with orange accents) Zune Theme was one of the most attractive UIs I ever got to use.
I can't find the xfwm theme, but it had a good balance between usability and "fun". That with some GTK theme such as the default for XFCE 4.6 looked fun to use without looking very childish.
Altough I must 'konfess' that the Keramik theme with the Noia icons and some handwritting font made reading advanced man pages in Konqueror a lot less "dramatic" and careless, thus, keeping the stress down.
Altough I must 'konfess' that the Keramik theme with the Noia icons and some handwritting font made reading advanced man pages in Konqueror a lot less "dramatic" and careless, thus, keeping the stress down.