Flora-de: Flora von Deutschland: http://blumeninschwaben.de/index.htm
Flora of Germany.
A large website with numerous photos of each plant species: 4,514 species of plants with 34.144 photos (April 2015).
The key ("Bestimmung") is copiously illustrated and easy to use.
Although the text is in German, modern web browsers do a good enough job of translating to make the site usable, though the keys can be a challenge if you don't speak German.