NZFF

There's a really good round-the-world hoplist on this server, there's always someone online too.
Address: 99.233.185.192

Likewise here WSPilots
99.99% of all my flightsimming has been done on those 3 servers in the last 4 years

Great bunch of guys, and I believe Russell **** (the guy who makes the FS-Host client software) is tied up with them somehow as well.