Official Diplomacy sets, variations and where to buy
The original Hasbro Edition is probably the physically best edition ever made - much better than the current US version with cardboard counters.

The other highly recommended edition is the 1992 Deluxe Diplomacy by Avalon Hill, which turns up very occasionally and very expensively on eBay.

The only professionally printed Dip variants I know of are Colonial Diplomacy and Machiavelli.