How can I make reserved slots for donators? For example, if the player limit is 20 players, it can have a 23 players on. 23/20 players. An example of this: play.itsjerryandharry.com They only have 1 slots, but a few hundred people online.
http://dev.bukkit.org/server-mods/loginlimiter/ In your example, just set the **global.limit** to 20, but your server.properties to 23. Then put your VIP perms into **global.limitExemptPerms** I think there's also a specific VIP login plugin out there if that's all you want.