For a direct replacement for the 17-85 I'd go for the Canon EF24-105
L IS f/4... good range,
L glass quality and image stabilisation make up a very nice package.
Whether it'd be wide enough for landscapes is something you'd have to decide, the 1.3x crop factor makes it roughly a 31-32mm equivalent lens which probably isn't ideal but may well suffice (*note* It would be about 4-5mm
less wide than your 17-85 was on your 20D).
If that's not wide enough I would take a look at the Canon 17-40
L f/4, you'd lose alot of the zoom but it would certainly be wide enough on the 1D.
I'll let others tackle the 50mm f/1.8 question, as although I think it would probably suffice I'm not really sure how much distortion it produces.
