[wavemachine]

It is a very difficult choice and really depends on what you want to shoot, I have the 15-85mm and it is a nice lens although it is not without it's issues suffers a bit from CA and barrel distortion but it is a pretty good compromise and a good walkabout lens. I did look at the sigma when I bought my 7D but it was a tad soft for my liking but that may have just been a poor sample of that particular lens as I have heard very good reports about them.

I think if I was in your shoes I would probably opt for the kit lens, find out what I like shooting and upgrade from there once I have got to grips with the camera. If you do go for the kit lens then I am sure you will find a use for it when you have upgraded or even still get a few quid on Ebay but it will buy you some time to decide what you want to do.

With regards to UV filters it is another element of glass if it is poor quality then it will effect the image I guess by going for a cheap one then you are taking a risk I guess you could take the gamble and take a shot with and without it and see what effect it has although I would be inclined to get a mainstream one, I have seen examples of filters which are poorly manufactured and have damaged the filter thread on the lens or have become jammed and have been very difficult to remove.

You are not restricted to skylight or UV though there are some ultra thin lens protectors as well.