Essentials-
So yeah, we all know about essentials. Ill list some commands/ how they work
/ban (player) (reason) - Obvious, ban a player
/kick (player) (reason) - Kick a player from the server
/mute (player) (time)(units) - Mute [player] for [time]
/jail (player) (jail name) (time)(units) - Jail a player at [jail] for [time]
/antioch - Spawn TNT where your looking
/afk - Marks you as afk.
/back - Teleports you to your last location before death/TP
/balance - Tells you your ingame money balance.
/backup - Backs up the server (only works if you configured it)
/banip (IP) - Bans (IP) from joining the server.
/broadcast (MSG) - Broadcasts [msg] to the server
/bigtree (tree type) - Makes a big tree where you are looking
/burn (player) (time) - Sets (player) on fire for (time)
/ci (player) - Clears the inventory of (player)
/compass - Describes your current location.
/near - Shows near players to you and how far they are from you in blocks.
/deljail - Deletes a jail
/delwarp - Deletes a warp
/depth - Tells your depth
/eco (take|give|reset) (player) (amount) - Deducts/Adds/Resets (player) balance.
/essentials - Reloads the essentials plugin
/ext (player) - Extinguish yourself or (player)
/getpos (player) - Get your current coordinates or those of (player)
/gc - Get RAM usage info from the server
/give (player) (item) - Gives (player) (item)
/god - Enables god mode
/heal - Heals you
/help - List commands
/helpop - Requests help from operators
/home - Teleports you to your home
/invsee (player) - Lets you see the inventory of (player)
/jails - List available jails
/jump - Jumps to the nearest block in sight
/kickall - Kicks everyone off the server except the issuer
/kit (kitname) - Gives you (kitname)
/kill - Commits suicide
/list - Lists online players
/lightning - Become thor
/mail - Send players mail or check your mail.
/me (msg) - Describe an action in context to the player.
/motd - See the message of the day
/msg (player) (msg) - Sends (player) (message)
/nick (nick) - Changes your nickname to (nick)
/pay (player) (amount) - Pays (player) (amount)
/ping - Shows server lag.
/realname - Shows a players real name rather than a nickname
/rules - Views the server's rules.
/seen - See the last logout time of a player.
/sell - Sell the item currently in your hand to the server.
/sethome - Set your home.
/setjail (name) - Creates a jail at your location named (name)
/setwarp (name) - Creates a warp at your location named (name)
/setworth (item) (price) - Sets the worth for an item when using /sell
/socialspy - Lets you see all /msg commands.
/spawnmob (mob) (amount) - Spawns (amount) of (mob)
/suicide - Commit suicide
/tempban (player) (time) - Temorarily ban (player) for (time)
/thunder - Change the weather to thunder
/time (day|night) - Change the time to day or night
/ptime (day|night) - Change the client side time to day or night
/pweather (sun|rain) - Change the client side weather to sun or rain
/togglejail (player) - Toggles if (player) is in jail.
/top - Teleport to the top of where your standing.
/tp - Teleport to someone
/tptoggle - Disable people teleporting to you
/tpo - Force teleport to someone
/tpohere - Force teleport someone to you.
/tpa - Request to teleport to someone
/tpaccept - Accept teleport request from someone
/tpdeny - Deny teleport request from someone
/tpahere - Request someone to teleport to you
/tpall - Teleport all players on the server to you
/tppos - Teleport to (coordinates)
/tree - spawn a tree where your looking.
/unban - Unban a player
/unbanip - Unban an IP
/unlimited - Allows the unlimited placing of blocks
/warp (name) - warps to (name)
/weather (rain|sun) - Changes the weather to rainy or sunny.
/whois (player) - displays info about (player)
/setspawn - Set where players spawn.
/worth - Tells the worth of the item you're holding
/world - Teleport to worlds
/spawn - Teleport to the spawnpoint set by the server administrators.

Look for my worldedit tutorial coming soon!