Copper Canyon and Topolobampo on the Pacific Coast. Overlooked by most foreign tourists, this is a very lovely part of Mexico that can be traversed by train.
Copper CanyonThat said... I would caution on travelling to many parts of Mexico right now. There are a lot of drug wars going on, there is very high crime and certain regions of the country should be avoided altogether. Myself, I wouldn't travel there for the foreseeable future.