Well for Landscape photography you are going to be looking at either a good quality wideangle zoom or prime lense with also a budget for a set of decent quality NDGrads.
For my landscapes I use a 10mm-20mm f/4 Sigma zoom lense and recently I have just bought a 17mm f/3.5 AT-X Tokina prime, see this link for a "mini review":-
http://www.trickery.net/vb/showthread.php?t=38060
The Sigma at 10mm really does do some outstanding shots for Landscaping but as you will see in my review it does have some minor shortcomings. The reason I bought a 17mm prime lense for Landscapes is that this is the equivalent focal length on my 350D as a full format camera has using a 90mm lense which almost all landscape photographers use. Another very good lense at around the wideangle mark is the Canon 17mm-40mm L zoom lense but this costs around £500 but it is very good, but imo it doesn't just go "wide" enough like the little Sigma can...
As for NDGrads you can either get the best and purchase a set of Lee 0.3, 0.6, 0.9 soft NDGrads (£100+ and necessary holder) or go for the 85 series HiTech ones in the same format for around £40 plus holder (you can use the Cokin P Holder with them), rumour has it the HiTech ones are made in the same factory, whatever you do don't be tempted by the Cokin NDGrads as they cast a reddish / brown tinge to your shots and are not really that neutral at all.
Also I noticed you haven't mentioned that you have a tripod or not, if you haven't got one yet this is probably as important as anything in Landscape photography and Manfrotto is a good brand, yet again make sure you dont scrimp on the purchase of this as the cheap ones are usually too light and will move in the wind etc..
To summarise:-
Good Wideangle Lens (10mm or above)
Strong sturdy Tripod
Set of NDGrads
Remote shutter release (cable or IR)
The light
See my Photoblog for what I am managing to achieve with the limited kit I have to hand
Russ
p.s. Also remember to shoot in RAW mode all the time in your camera and do the exposure and WB settings in something like Capture 1 Pro or the free application by Pixmantec.