Oh well. Some days ago I found some numbers from the electricity company EnBW which runs the power grid in the whole Bundesland Baden-Württemberg (and some more).
According to their brochure (http://www.enbw.com/content/de/netznutzer/media/pdf/TNG_Imagebroschuere_deutsch.pdf) they run 1970 km of 380-kV-lines, 1674 km with 220 kV and 56 power stations (not counting those that only have 110 kV). Btw, the brochure also has a nice map of this part of their net.
If that isn't enough, there are 7600 km with 110 kV according to this web page: http://www.enbw.com/content/de/der_konzern/enbw_gesellschaften/regionalgesellschaft/zahlen_und_fakten/index.jsp
That's quite a lot, even if I just look at the lines that are within reasonable distance from my home.
So, still a lot of stuff to map. I'm not sure if that's good or bad though. ;-)

The most interesting ones for me among the big ones are
-the famous Nord-Süd-Leitung (finished in 1929!) from Brauweiler near Cologne to Bludenz in Austria. The section between Hoheneck (north of Stuttgart) and Herbertingen (in the Danube valley) has already been done by other people, mostly from Yahoo images I think. But there are still things to discover like the brand-new branch that goes to Metzingen which I discovered just last weekend.
-the 380-kV-line Hoheneck - Wendlingen - Laichingen - Dellmensingen (south-west of Ulm). One half is run by RWE and the other by EnBW. The first piece after Hoheneck is still missing, otherwise it's complete up to Dellmensingen.