We've done most of these trips and highly recommend it:
Domestically
1) Portland, ME and the surrounding area - incredible food scene in Portland, ME!
2) Drive from San Francisco, through Napa, stopping by the Yountville mecca of course, up the coast to Portland, OR. Portland OR has an incredible food scene - serious people making incredible eats!
3) Houston - yes, you heard it here first - Houston's food scene is diverse, with tons of ethnic eats as well as fine New American dining
4) NYC, of course....but why not also drive to Flushing for amazing Chinese food and since you're already in the vicinity, pls drive to Connecticut for the Pepe's vs. Sally's pizza taste-off
Internationally
1) Spain & Morocco - this trip will guarantee a diversity of flavors - European into Middle Eastern/North African
2) Japan - go with someone who speaks the language - it will help greatly, as we learned on our second triip there!
3) Eating tour of South East Asia - start in Singapore, work your way up to Malaysia and/or Thailand, followed Vietnam and/or Cambodia - on these trips, I like to do the fine dining (you still get a lot for your USD) and street food - fantastic contrast!
4) Sri Lanka & India - I'm planning this trip for next year
5) Italy, of course!