I am trying to get it to 100 asap, whats the best way to do this? I don't care if its a cheat either.

Here you go http://elderscrolls.wikia.com/wiki/Sneak_%28Skyrim%29#Leveling_Tips

I'm sure there's a console command for PC.

I got mine pretty high by just Sneaking. It seemed to go up faster if I was slightly moving right as the eye was closing...could've been coincidence though.

Trainers:
Khayla (Adept): Khajiit Caravans
Garvey (Expert): Markarth
Delvin Mallory (Master): Thieves Guild, Riften (most likely have to join the Thieves' Guild for access)

Also, there's an amulet (I came across it randomly) and:

Spoiler:
If you kill the Dark Brotherhood leader you can get her hood that gives a bonus.

I'm not sure if items help you level abilities, but they might since you are technically Sneaking at a level higher than what you've attained so it may count as being more difficult.

Don't care if it's a cheat. Okay then. On a PC? type this into the console:
playerenchantobject 000cee84 0001ea6a

It gives you a Fine Hat that makes you invisible. Put it on, crouch down someplace crowded, and wait. Your sneak skill will steadily increase.

I'm a dual wielding, heavy armor type, and sneak is one of my highest skills, if not the highest. Its very easy to increase, I just sneak around every dungeon I find.

EDIT: I'm level 11, by the way. That's ridiculous, its not even funny.

1. go inside someone's house.
2. crouch behind the corner where they can't see you, preferably close the door behind you.
3. press auto-move key.
4. go make yourself a sandwich
5. go for a walk outside
6. take a shower
7. your sneak has maxed

Got it to 100 by whacking on greybeards with sneak attack and healing them after 3 hits for 45 minutes

There's also a cave near Whiterun with a blind guy just inside. If your sneak is really low, you might need to use Muffle at first, but aside from that just sneak (walking) on auto-run into the wall behind him, and go take a nap.

Me too. Talos would be ashamed of me.