These may be the most recognizable sweater once the movie comes out, it is the sweater worn by the Gryffindor Quidditch team under their Quidditch robes (which are scarlet on the outside and gold on the inside). The sweaters appear to be either stocking stitch or a 2x2 rib, but since they were made on knitting machines instead of by hand, the ribbing is different. A 2x2 rib would pull in tightly, which is not how these sweaters lay. Some ideas for knitting this sweater by hand would be to use shaker or double knitting to get the ribbed effect, or to just ignore the ribbing and knit it plain. You can see a detail of the collar on the top picture, which shows us that these are crew neck sweaters with the gold detailing at the base of the neckline. We can probably assume that the wrists also have the same detail. (note that in another picture, the bottom of the sweater is visible and there in NOT a gold stripe at the bottom, which is not fitted but lays fairly straight) The stripe on the chest is wider than a typical striped sweater (the ones which were so in style 2 seasons ago), and is also placed lower to allow the space for the house badge. These are drop shoulder sweaters but that detail probably isn't too important to non-knitters.
If I were making this sweater, I'd make it top down in order to determine the spacing. For the badge, you can go to any Warner Brothers store and buy something with the badge on it, then cut the badge out and sew it on (thanks to Marion from the KnitList for that idea!). I'd start from the neck, knit enough space for the badge, then start the gold stripe, making it about 5" wide. That is probably the hardest part of this sweater, any old pattern would work!
Another Note: This sweater is also not mentioned specifically in the books, which only mention "uniforms" and "robes" when describing Quidditch clothing. They do look great, though! And we can assume that the other houses have the same sweaters, in their own colors. There are no stills as of yet of the other houses' quidditch players, so we can only guess what those uniforms would look like.
Update 12/11/01: I added a picture of the Gryffindor house badge that I found on eBay. I think that clarifies what it looks like really well, doesn't it? =)