Morning,
Well I have gone down the wide angle route for quite some time, and have acquired glass along the way for specific reasons and quests. Professional landscape photographers usually wind up using 24,28 to near mid 35mm lenses due to the lack of distortion, as folks have talked about here already. What you are going to get by supplementing your 18-55 kit is not a different view, but higher image quality, resolution, better distortion control, maybe a faster aperture (to a degree), etc. be it at the associated cost. You can start helping yourself out by perhaps sorting your current shots from the kit lens by focal length (there is software to do this for you), and seeing what focal length has appealed to you the most. That would be a starting point.
In terms of "field of view", the lower you go in focal length, the wider each additional mm gets. That is the upside. The downside is that in order to obtain that additional mm, you are bending the light to get it on to the sensor, that bending brings with it additional distortion around the edges and boarders. Not a thing you can do about it, except to figure out how much - is too much for your taste.
So before I go on, let me add one comment here that I have not read yet. Your camera has a sensor of a fixed size (for the sake of argument lets say 4000 x 3000 pixels). As you walk through the focal lengths that you put in front of this fixed size sensor, each pixel will represent an area within the image. This pixel's representation of this area (which is length x height - 2 dimensions), will vary from a very wide angle lens to a more normal lens. As an example, the area represented by an individual pixel will have about 4x as much area at 8mm than at 30mm. Due to this, the more normal lenses are going to have a "sharper" quality to them, as opposed to a wider lens. This is something that folks don't consider, as in what goes into getting that wider field of view. Layered on top of this is the distortion issues of the focal length.
Originally I went with zooms for the versatility.
- 10-17 Fisheye - is excellent - and one of my favorites. Great colors and rendering. Through composition, you can put the "bend" where you want it within the frame. Works very well on natural objects where the bend/distortion is not as obvious.
- 8-16 - wonderful lens, great rendering and it is wiiiidddddeee - perhaps a bit too wide. Perspective control can be a problem if you put the subject tooo far towards the edge. Framing and composition is important. One thing I like is square rigged tall ships. With its 117 degree field of view, I can get the top of the mast to the waterline in one shot, relatively close in.
- 12-24 - is also excellent and again one of my favorites. When in doubt - I use/take this as a single lens. Its not as wide as the 10-20s or 10-24s, but it has a wonderful balance between distortion control, great resolution. Sweet spot is about 18mm.
- 16-45 - Again an excellent lens. Its going out of production, thus its price has been cut in half down to about $225 or so. Complements the 12-24 very well.
I have also acquired primes due their image quality. The zooms are great, however the primes coupled with their focal length are superb.
- Zeiss 25/f2.8 ZK - Wonderful resolution, color and rendering. Very little distortion. Relatively fast at f2.8, and for me has an added close focus at 6 to 12 inches consumes 180 degrees of barrel turn of the 355 degree possible for focusing.
- Contax Zeiss 28/f2.8 - I swapped mounts on this lens. Excellent, small and very light all manual, a poor man's 31 Ltd.
- 31/f1.8 Limited - What everyone has ever said about the lens.
In essence, I have used the zooms for the very wide, and the primes for the low distortion standard landscapes.
Now one additional aspect to all of this. When you talk about wide angles, one unsaid aspect to all of this is foreground. With wide angle lens you get foreground, lots of it. Norm was talking about hanging off the edge of a cliff to get a shot. Well in this case I would think that the foreground was all the scene of the valley or gorge in front of him. Normally, you have stuff in front of you. The WA lenses will put it in to your frame, and you need to compose around it, or find something interesting to put into it. Just water or beach all the time becomes very boring. Another approach is to 1) crop it out (but you just paid a small fortune to buy the lens) or 2) shoot over it, with a longer focal length. Something like a 50, 85 or 135. Folks usually don't consider these as landscape focal lengths or lenses.
One more thing - stitching. You can stitch wide angle images together (including fisheye shots). I stitch wide angle shots together all the time to get both wider and deeper. That also goes for the not so wide focal lengths.
hope that helps....