Originally posted by Marc Sabatella ....
If the problem is simply that the 18-55 isn't wide enough even at the 18mm mark, then the 21 won't help either - you need something wider than 18mm. So the DA 12-24 or Sigma 10-20 are both good options, and so might the new DA15 or the DA14 if you should decide that you want smaller size (DA15) or larger aperture (DA14).
I can talk about the 12-24. It is a great lens. About the new DA15 or the fast DA14 (I dont have either one) I would think twice about this two lenses before, considering the following:
1) The new DA15 is small, but optically questionable, since a couple of reviews have stated that even the DA 12-24 zoom has far better image quality. That is a BIG STATEMENT to say that a zoom has better IQ than any prime.
2) The DA14 f/2.8 is two stops faster than the new DA15. It is also a bit wider and it sells for the same price of the DA15, and about the same price of the DA 12-24.
3) Both the DA14/2.8 and the DA 12/24 zoom are about the same size (bulky). The only thing in favor of the new DA 15 is size (and probably construction).