Great news for Portal 2 fans : 

Valve’s Doug Lombardi (VP of Marketing) let it slip on FastCompany, saying: “We will be announcing some DLC for it, so folks can keep a look out for more content coming this summer. We’ll be putting more details out about that in a week or so. We’ll support that with more videos or more comics.”

http://www.godisageek.com/2011/04/portal-2-dlc-coming-summer/

The full interview with Erik wolpaw and Doug Lombard - which contains loads of Spoliers is at:

http://www.fastcompany.com/1750003/portal-2-valve-eric-wolpaw-jeep-barnett-doug-lombardi

I hope it's with full scale voice work and a little story (I'd pay for that) - but any new maps and Co-op would be cool (if free) Can't find any more details yet.

Edited 29/04

UPDATE :  Details of Free DLC

Headed to all platforms (PS3, PC, 360 and Mac), Valve is currently calling it "Portal 2 DLC #1", which will bring new test chambers, leaderboards, a new challenge mode for single and multiplayer modes, "and more". That already sounds like plenty, but we'll take more if you're offering, Valve. 

And guess how much that lot will be. Free! The best kind of price.

http://www.computerandvideogames.com/299762/news/portal-2-dlc-details-new-chambers-challenge-mode-more-free/

Edited 02/05/2011 User Created Maps

For people interested in User created Maps both for Co-op and Single player for the PC there is a great site called http://www.thinkingwithportals.com  if you need any help just ask in this thread.

If anyone else has knows of any sites that host Portal 2 maps post it here and I'll update this thread.

E3 announcement I assume. GlaDOS at the sony conference again???

After doing some reseach I found a nice little site : http://www.thinkingwithportals.com/

People are already doing some early custom maps without the SDK (which won't be out for a couple of months) haven't tried them out yet but there is about 4 single player maps out and a  10 level co-op (including a hub). PC only and you have to access the ingame console as the menu doesn't yet support them.  The maps come with a Readme.txt to explain how to do it.

(Going to try them out tomorrow - love the royal wedding ) 

Who says you have to buy it? ;)

do you think the ps3 version might get it Free?

PC will be most likely free unless it's a full episode.

Ouch... Didn't think of that (in time). But it's a choice you made.

Just give me more awesome quotes like (and I may be paraphrasing here):

"Here come the test results; you are a horrible person. That's what it says, you are a horrible person. We weren't even testing for that."

"I'm serious, visualizing the scenario while under stress actually triggers the reaction."

And I'll be happy.

Headed to all platforms (PS3, PC, 360 and Mac), Valve is currently calling it "Portal 2 DLC #1", which will bring new test chambers, leaderboards, a new challenge mode for single and multiplayer modes, "and more". That already sounds like plenty, but we'll take more if you're offering, Valve. 

And guess how much that lot will be. Free! The best kind of price.

http://www.computerandvideogames.com/299762/news/portal-2-dlc-details-new-chambers-challenge-mode-more-free/

I just discovered that Stephen Merchant did one of the voiceovers, well I really consider buying it since it looks better than Portal.