This blog has a few marathon-realted posts, and Iliked this one about alternative marathons
http://www.runflux.com/blog/2007/10/...arathon-races/
One poster nominated Amsterdam, which I have done and thought was pretty good. Have done barcelona, and wished I'd just gone for a weekend break withoiut the marathon - most of it seemed to go out into dull suburbs and industrial areas...
Good luck!