As by now everybody knows there is a volcano erupting on iceland (Eyjafjallajokull) that has brought down most air traffic in Europe. As annoying as that can be to travellers (and I have several friends stuck because of it) it does give rise to beautiful images. Later there will be some really nice sunsets and sunrises too because of the volcanic ash in the higher atmosphere. There is a really nice gallery on the big picture here. They show and link to extraordinary images from Belgian photographer Olivier Vandeginste. Well worth a look.
Earlier Big Picture gallery
The Frame 1
The Frame 2
Denver Post (love that picture of the icelandic horses before the cloud
NY times lens blog Superb images!
I like this image from flickr user Sverrir Thor, who has many more nice ones in his stream.