Well, in 2006 I spend about $5k on a month long back packing trip through Western Europe. I figure with $10k I could repeat a similar journey with my wife and bring her along. I'd visit a few of the cities I've already been too that I loved, and skip some of the ones I didn't really enjoy. Definitely travel by train. I'd definitely hit up Amsterdam, Nice, and Prague again, and probably spend some more time in Switzerland and try to make it to Budapest. You can really stretch dollars in Prague and Budapest.

I would also say SE Asia, but my wife has never left the country outside of going to Canada, so I think she needs to ease into experiencing other cultures, and Europe is a good start. I would love to go to Thailand and Vietnam, but as others have mentioned, there's some tension going on in Thailand currently. That wouldn't scare me away, as I'm sure it's just local to parts of Bangkok, but I don't think I could ever get my wife to go there... not yet.