How do I spawn mobs in SMP?

As of release 1.1, you can enter Creative mode and use the new "Spawn Eggs" item to produce monsters, even in vanilla.

You can do it in bukkit with the /mob command.

http://dev.bukkit.org/server-mods/admincmd/pages/mob-commands/

http://dev.bukkit.org/server-mods/admincmd/

I spawn eggs on my server (it's vanilla, not Bukkit!) with /give (name) 385 (mob id)