Hi Pete
I use a hood most of the time, and purchased the genuine Canon ones for both my lenses from ebay. I think they came from Hong Kong or China, are the genuine article, and cost about half the uk retail price. Each hood is tailored to the focal length of the lens to ensure you do not unintentionally get corners cropped off your photos when shooting at wide angles.
Filters is a bit of a mine field, but I was guided by Bruce, who I consider to be something of an expert in these matters, and they have proved almost essential for landscape work. You can get cheap filter kits, such as Cokin, which I started with, but I quickly realised the quality of these is pretty poor. I'm not too sure how the polarisers fair, but with regard to the neutral density grad filters I bought, they leave a horrible magenta cast on the image.
I went for the Lee filter system in the end, but they are horribly expensive, though all hand finished and of excellent quality. I have a polariser and six ND grad filters (0.6, 0.9 and 0.9 in both hard and soft graduation). If you only buy one filter, go for a polariser as for sky, water, reflections, glare etc they are indespensable, and are about the only filter effect you cant properly replicate in editing software.