The North Sea Cycle Route. Follows roughly the North Sea from France across Belgium, Holland and Denmark, into Scandinavia then across to Scotland and southward through England to finish... in France.
I followed some of it in 2003, and I have a desire to go back and do more. It is reasonably well marked and takes in a variety of bike paths, trails and roads. It IS about 6,000km in total, so it does take a few bites to do.
Oh, and for something really spectacular, the Canadian Rockies. I was there again at the weekend, and I still can't get over how magnificent they are. Definitely something Australia cannot match. Youprobably wouldn't get a 1500km tour out of them, but then there is Alaska as well...
The Canadian Maritimes do appeal as does Nova Scotia. One day I might get there.