Update: Ive seen some very nice logo entries so far. For the people not in the top rankings: A combination of an abstract character, reference to construction materials (helmet or gear or bricks but not restricted to those two, anything related is good) and integration of our business name in the logo (this I have not seen - an example would be a hammer smashing the . on the i in our business name) is the base for succes... Oh, and do not forget a touch of blue since this is how the site will look like:
http://development.pixelconception.com/magento_construction/