Tohoku is a neat low-detailed map but has limited airports and is quite small.
Hawaii is a favorite for airlines and features a wide selection of airports, but it can be a bit hard to get your bearings and it still doesn't allows for really REALLY long-haul flights.
The Philippines is a new add-on with stunning detail, size, and airports, with a wide selection of airports and enough room for some seriously long flights (as far as nice maps go). However low-RAM users, or users with bad graphics cards or the wrong program (OpenGL or Direct3D) can encounter lag and SHAKING


Canary Islands are nice and compact, with a good choice of airports, but it's not quite as big as Hawaii, and *again* doesn't offer true long-haul (for YSFLIGHT) routes.
There are others too, but these are the 3 I can think of and it seems like a good list.
Thanks welshy for the Canary Islands add.