I've shot all three formats quite a bit, as a landscape photographer, and here's my take:
35 mm film is out of contention against any digital SLR at or above 6 MP. Note that 35mm will outdo any digital COMPACT I've ever seen, due to dynamic range (digital compacts are very poor, while digital SLRs are quite a bit better).
The very wide dynamic range of 35mm (and 120) negative film is tricky to scan, trickier still to print. Slide film scans better, but has no dynamic range advantage over a good digital SLR.
Nikon's 10 mp digital (I've used the D200 extensively, which has basically the same sensor as the D80) falls somewhere between 35mm and 645 image quality, clearly inferior to 6x6 cm well scanned (Nikon 8000 or 9000), but just as clearly superior to 35mm Velvia.
The only digital I've seen that beats 6x6 cm is the 17 megapixel 1Ds mkII (which is equivalent to 6x9, as best as I can figure). I've never used a 5D, so I can't comment on that camera. The 1Ds mk II also has better dynamic range than most other digital SLRs.
While the Rollei has the best image quality of your options, I'd be tempted by the D80 for convenience's sake, depending on where you're going. Also note that you can carry a ton of exposures for your D80 in a few very small memory cards, while 120 film gets bulky!
-Dan
