What to have as secrets?

And you didn't even spoiler tag your own level.

So?
The hard bit is finding it, And then getting to it.
I mention it in the level's post, FGS, its not a big secret, more like a hard-to-find-area-that-makes-you-feel-happy-that-you-found-the-damn-thing

I think a good secret is extremely humerus, in a blatant type of way (not the path to the secret being blatant, the secret itself)

e.g: OMG A SECRET!

I kinda like The Squashed Orange's
"Secret area FTW" myself

In my opinion a secret must be worth finding. A reward is much better then a congratulations message.
Here are some ideas:
* Have one of the four colored keys in secret area.
* Have a hint to something (Like a hint to a bigger secret).
* A teleportation system that can teleport to all areas in the level.
* Secret ending!

But a funny message is also nice. Like in A strange dream.

I kinda like The Squashed Orange's

Spoiler: Sahara secret (click to show/hide)

"Secret area FTW" myself

You know, you really should spoiler tag that. The Squashed Orange might not want you revealing it.
As for what to put as secrets, something random, a key or power-up needed to get to a secret ending, or even just a screen with someone saying something is good for me.

* Have a hint to something (Like a hint to a bigger secret).

That leaves the problem of what to put in the bigger secret.

Personally, I just make an area that is obviously NOT part of the level, often quite silly.
Take happyland in FEAR for example. The level is all dark etc, but the secreat area is a big green smily face on a rainbow background.

and when i saw that the first time i was like, what the heck? and then i couldn't escape from it

in caverns I put