ItsAllOver
Devil's Advocate
I was looking at YouTube videos about this hidden rooms and spaces, and came to a couple videos of this brand of hidden doors. (videos in the Products section of the site) They are pretty cool, but I bet they're expensive.
It'd be easy enough to DIY something like this, depending on your carpentry skills.
Here's a company that does a little more custom jobs than above... I highly suggest you watch that video
I have seen people here on ICmag (shout to: Lightning Bug) turn the first part of a bedroom entrance into a closet, which was another nice stealthy way to keep guests out of your grow.
There are some books on Amazon that I've found interesting, too...
Secret Rooms, Secret Compartments
How to Hide Anything
How to Bury Your Goods
How to Implement a High Security Shelter in the Home
And while we're at it, why not
Carpentry and Construction
for those that need that link, too, to get them started in the right direction.
Just thought I'd post this to spark some imaginations...
Anyone have ideas?