I guess I'd go for the 5D MkII unless you need the higher level of environmental sealing of the 1Ds MkII. The 1Ds MkII might also have the edge in AF performance too.
The
5D MkII is cheaper at around $2700. The
1Ds MkII seems to be selling for around $5000, though Adorama have
1Ds MkII refurbs for $4000Image quality seems pretty much equal with maybe a slight advantage to the 5D MkII, and the 5D MkII has HD video, even if you don't really need it right now (one day you might).
So overall I can't really see the 1Ds MkII being worth the extra cost. I'd get the 5D MkII and spend the rest on a nice lens or two!