The Emotiv EPOC is a relatively cheap ($300) EEG headset intended for gaming.
I have considered buying such a device for some time. Unfortunately, the device is sold out at the moment and only available in the US.
A developer headset ($500, sold out, too) is available worldwide. However, you would need to purchase an SDK, ranging from $500-$7500 in order to do anything meaningful with it. The SDK does not support Linux, of course.

However, today Cody Brocious (Daeken) has released the first version of a Python toolkit for the EPOC. For this he cracked the AES encryption and partially reverse-engineered the protocol.
There’s still a lot missing – for example, it is not clear which signal belongs to which sensor, and the signals are not yet analyzed in any way.

This seems like the right opportunity to get an EPOC and tinker with it. Thanks Daeken.

Some discussion is happening at Hacker News and Hack A Day

Update: H+ magazine has an interview with Cody, conducted by Bryan Bishop who already wrote a Python wrapper for the EPOC in June, using the official SDK, however.

Update 2: It seems the developer headset is different from the standard one. skadge is trying to get it working.

Update 3:
Emotiv responds in their forum:

We strongly oppose this kind of action. It violates the end user license and seriously threatens our viability. It is no exaggeration to say we may be forced to withdraw the consumer headset from the market or go out of business entirely. Kinda defeats the stated purpose of “opening up” the product for research users – which is frankly spurious because it IS open to properly licensed owners – and OpenViBE has a properly licensed driver already in Beta development.

It’s all well and good to demonstrate how smart you are by hacking the iPhone – Apple can afford to lose some revenue. We are a struggling company and this action has prompted our investors ask us to show cause why they should not demand repayment of our operating loan. Research licenses are a substantial part of our revenue. Thanks to this selfish action we may well have to close the doors or withdraw the consumer product, or re-price it at a significantly higher level.

That enough discussion for you?

Update 4:
Daeken has posted an unconfirmed Dev Key on IRC:

conKey = '\x31\x00\x35\x54\x38\x10\x37\x42\x31\x00\x35\x48\x38\x00\x37\x50'
devKey = '\x31\x00\x35\x48\x31\x00\x35\x54\x38\x10\x37\x42\x38\x00\x37\x50'