Below are 8 minimal GTK2 themes for your Ubuntu desktop. To install them either follow the instructions given or use the ‘Appearances’ dialog from the ‘System’ menu.
MurrinaStudio
http://drfr4g.deviantart.com/art/MurrinaStudio-78479558
T3K
http://amadme.deviantart.com/art/T3K-103862094
Gaia Neue
http://fratrip.deviantart.com/art/Gaia-Neue-Suite-100383098
KUPO
http://lassekongo83.deviantart.com/art/Kupo-Finale-107870797
Tuxido
http://lassekongo83.deviantart.com/art/Tuxido-78008931
Luder
http://lassekongo83.deviantart.com/art/Luder-87861498
Pukco Modern
http://lassekongo83.deviantart.com/art/Pucko-Modern-101791479