So, I discovered something amazing in the new snapshot(12w34B). You will need;
-Basic redstone knowledge
Step 1: On a server, make a redstone repeater. Any kind should work.
Step 2: Type in chat; "/give (name here) 137 64"
Step 3: Type in command block UI; "tp @a @r" and connect the command block to the repeater.
Step 4: ????????????
Step 5: Profit!
I didn't bother adding pictures because it's kind of hard to show this with pictures and isn't as funny when it's not happening to you and your friends.
Another idea is to set the repeater to "/gamemode @a 0" and surround the device in bedrock. Funny if you're playing in creative mode.
I might add some more suggestions later but i'm sure you can figure some out for yourself. (Hint "me @a SAMPLETEXT")
Anyway, my friend is yelling at me to play Magicka. Have Fun!