Need sharp wide lens for landscape photography

OK, been searching the forums for information on the right lens for me. I WOULD like to buy the 17-35 but cant afford it right now and think you can get att good lens for about half the price. I now shoot mostly with my ket lens but my pics allways end up at the lower range, from 17-28 (or mayby 35) and I dont think the kitlens give my enought shapness at this lower range. I also own a 50/1.8 and a 70-210 (an almost classic starters kit). So I have been looking at some lenses:
Sigma 15-30, 17-35, 10-20
Tokina 12-24, 17-35, 17mm ATX
Tamtron 17-35
Nikon 18-35, 20mm, 24mm, 28mm, etc

whats is your recommendation and what should I consider when picking a lens for this purpose? Remember, my wallet is limited? I Want tho get really sharp and contrasty images.

I post som sample images from my favorite range, around 20mm. (pics have been PP and sharpened)

(22mm, F9, 1sec)

(18mm, F8, 1/60sec)
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My Photos: http://www.pbase.com/fam_morck
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