Well, the best lens in this category would be the Canon 17-55 F2.8. But if that is a little out of your budget, the next best lens is the Sigma 18-50 F2.8 Macro, with the Tamron 17-50 F2.8 following the Sigma.
Are third party lens hoods any good as long as they twist and lock onto the hood mount of the lens? I'm looking for a hood for my Nikon 80-200mm F2.8 (the HB-7 hood) and I'm seeing a lot of hoods closely resembling the HB-7 for less than half the price. Does it matter?
DSLRs are for pictures, video cameras are for video. Do you want to take video, or do you want to take pictures. If you absolutely must have video, then I guess a Nikon D90 will work, but if video is such a priority then why are you getting a DSLR in the first place?
The fact is, to do the type of photography you want to, its going to costs many thousands of dollars. The absolutely cheapest route (while trying to to compromise with cheap kit zooms).
For landscape: Sigma 18-50 F2.8 ($400)
For Macro: Sigma 105mm F2.8 ($400)
For wildlife: Canon 400mm F5.6...
If you're looking for a superwide, the Tamron 14mm F2.8 goes for around $600 used. I hear its a very high quality landscape lens, although the front element protrudes like crazy, making filters a no-no and damage very likely in the event of a drop.
Manual focusing can be a real pain sometimes, so I would recommend a high quality zoom. The 18-70 is an excellent kit lens. However, it is a kit lens. The 17-35 F2.8-4 is more of a semi-pro/advanced amateur lens. For quality, the 17-35 is the way to go. I also believe it is a full frame lens...
Its a great lens, especially if you're shooting landscapes, and planning on going FF sometime in the future. It is an L lens, which means it will hold its value over time, not to mention the superb optical and build quality.