A sling bag is sort of a cross between a backpack and shoulder bag. It rides on your back like a backpack and usually has an auxiliary strap to keep it there when you're being active. Unlike a backpack, you can unclip the auxiliary strap and swing it around front to access the camera (like a shoulder bag). You don't have to take it off and put it down like a backpack. The access is generally through one side so that the access panel is on top when you swing it around in front.
You can also swing it around in front to ride a chairlift.
Sling bags have the disadvantage that all weight is placed on one shoulder. The shoulder strap is generally of backpack quality, though, and a 350D with the kit lens shouldn't be too heavy.
Sling bags are made by a number of companies (Lowepro, Tamrac, Kata, Thinktank, Case Logic, etc.). I use a Lowepro Slingshot AW 102, which is, remarkably enough, available in the local Wal-Mart. I don't know if Wal-Marts in the States will have Lowepro items, though.
Link is: http://store.lowepro.com/slingshot-102-aw
In my AW 102, I have:
Nikon D7000 with 18-105 kit lens mounted
Nikkor 70-300 zoom
Panasonic waterproof compact in its own padded Wal-Mart case
various small accessories
I liked it because it was small enough to grab and go, and I can ski, bike and kayak with it. Many alternatives either swing around too much (the Lowepro is stable with the auxiliary strap clipped in) or they would ride underneath the spray skirt of my sea kayak.
You may find that something a bit smaller works well for you. If there is extra space, it can be used for things like lunch or a stuffable rain jacket. You may also like a holster style, as long as you can secure it to your front or back rather than just carrying it like a shoulder bag.
For air travel, I use a larger shoulder bag that also carries a flash, laptop, back-up drive, keys, manuals, documents, passport, etc. That way, I don't have to empty my pockets for security because everything is in the camera bag. It weighs a ton when loaded, and it clearly shows that this hobby is getting out of hand! Gear lust can be just as bad for the photography habit as it is for the ski habit.
Have fun. Take the camera everywhere, shoot thousands of pictures, delete most of them, be pleasantly surprised at the good ones, figure out what made them good. It does require entirely too much time in front of the computer, though...