I don't know what camera you have but if it is one of the crop cameras eg Canon 20D, 400D or a  Nikon then you will be hard pressed to get a better lens than the Sigma 10-20mm for wide angle landscape shots. 

Don't forget to budget for good filters and a sturdy tripod too.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html