This is Sol's mutherfucking command guide for Minecraft. Hashtags are locations. Bold are things that are in the new snapshots.
PLEASE DO NOT ATTEMPT TO DO ANYTHING CRAZY WITH THESE COMMANDS. YOU CAN HOWEVER MAKE SOMETHING THAT TELEPORTS AWESOMESWAMPY TO 0 0 0 OVER AND OVER AGAIN!
The Summon Command
/summon EntityHorse # # # {Type:3,ChestHorse:1,Tame:1}

/summon EntityHorse # # # {Type:4,ChestHorse:1,Tame:1}
And no you fucks, I don't know how to summon other mobs riding on them. My server's a fucking lag bitch when Chrome is up so I can't search.
But so it's out there, any mob can ride any mob.
SO FUCKING VILLAGERS HUMPING IRON GOLEMS WOOOOOOO MINECRAFT PORN
BUT I CAN TELL YOU HOW TO SUMMON A GIANT
/summon Giant # # # {invincible}
Now go fight him!
(If you don't use {invincible}, it still works. It's just not as trolly.)
And for you squid haters,
/summon Squid # # # {invisible}
There you go.
Command Blocks
To get Command blocks, use /give (name) 137 1.
To get a command block cart, /summon MinecartCommandBlock and middle click it.
Crash Your Friend's Server
Get on dat server bb
Put the Minecart command block down.
Make a huge trail of tracks, with the activator one at the very end.
Set the command for the command cart: /tp Notch # # #
Let it ride on.