The new Opera logo looks really nice and so does the 2011 Office for Mac icons. What style are they?
This kind of logo is generally referred to as 'ribbon style' because of the way that the letters seem to be made from a folded or curved ribbon.
The examples that you have mentioned both use stylised versions of this approach, but the basic principle is the same. If you do a search for 'ribbon style logo' then you should find lots of examples and even a few tutorials.