Need to know what, where and how you're going to use the camera.
If you looking for a set-up that will let you shoot photos that can be published in photos then you'll realistically be looking at a Canon or Nikon system. I know other companies make good camera bodies but the range of available lenses for these bodies just isn't as broad in application and quality (unless you want to spend silly money on medium format cameras like Hasselblads, but we talking over 10Gs here!).
But do you really need such a system? Pentax make a range of SLRs that are a lot smaller and lighter than the Canon or NIkon SLRs. I haven't used one but have seen some pics from one and they were pretty good. They can also shoot RAW which is critical if you want to do serious image processing with Photoshop or whatever.
But...these smaller SLRs do have some downsides, most importantly in the range and speed of the lenses available for them. If you want to take photos where the background is blurred out and the skier (or any other subject) really 'pops out' of the photo then you need a 'fast' lens. Camera lenses have a range of 'speeds' (not a particularly accurate description but it will do) and the 'faster' the lens the better it is will be able to make the subject stand out in the photo and the better it will be in low light and with fast targets. On the other hand these high speed lenses are highly priced so if you don't want to drop that sort of cash then its not as much of an issue.
The quality of your photos will be just as dependant on your lenses as your camera body. I have an EOS 5D mark 2 but if I put I mid range lens on it all I'll get are mid-quality pictures regardless of the fact that the body is arguably capable of producing the best pics you can get for a system costing less than $10,000. So buying a great camera body but not having enough money to buy a decent lens for it is a waste of money.
If you decide you want a camera that can shoot photos worthy of being in a magazine or catalogue then it might be worth buying a slightly out of date full size SLR body (e.g. EOS 40D or Nikon equivalent) and using the money you save over a 50D to buy a nice lens to go with it.
Alternatively, if you want a camera that's reasonably easy to carry around and shoot photos that are good enough to impress your friends ands family (and maybe even some smaller sized photos for publishing) then perhaps a smaller SLR will work best.
Oh yeah, the Pentax shoots 720p video I think, as might others in the new range of mini SLRs (I'm not that up to date with these types of cameras).