I looked around the web quite a bit, and talked to the lens experts at my local store, before choosing lenses for my 300D. Although I originally planned on going with the 55-200 to match the 18-55 kit lens, anecdotal evidence seemed to indicate that the 55-200 isn't a really good deal.
For >$50 less, I got the 75-300mm. There are three versions of this - an IS (Image stabilizing) version, a USM version (non-ring-type, though, so no full-time manual focus), and the vanilla version (which is what I got). All three have the same optics (other than the IS stuff) - it has pretty good glass, for a lower end lens. I think it's a fantastic deal, particularly since with the 1.6x cropping factor it's effectively a 480mm lens (!) at the long end.
I bought this lens specifically for pretty much the same thing as you want - photographing wildlife topside. I think it's a good flexible telephoto, and I don't miss the 55-75 gap anywhere near as much as I thought I would. Bob Atkins has a good overview of available lower-end lenses on photo.net that you might want to take a look at - http://www.photo.net/equipment/canon/300D/...00D_lenses.html.