I reakon Coruscant is a good bet.  When we see Dooku vist Sidius it was in the same firey/industrial part of the city where Anakin and Obi flew over the lava.  

They've already said that the fight takes place through a number of sets/rooms i.e. not just on a vulcano but within a building that has lava in/around/beneath it.
So coruscant is my hot favourate, but with the promise of so many new worlds it could be anywhere.  Lets just hope its not in a lava pool where the workers are trying to get the Calibar crystal under Anakin's command, and Obi stumbles across it and tries to stop them.  No crystals! No crystals! No crystals! Come on, chant it with me, No crystals!

the info's from 18 July set diary in Hyperspace on the official site.  Take a look there for the full scoop or I have included the important passages below.

a scene shot today was originally set in Palpatine's Office. A quick rewrite kept the scene intact, but changed the venue. What was originally a private meeting has moved into a very public space.

After a morning of shooting in Palpatine's Office, the camera crew moves to a very sparse set on another stage. It's what people generally imagine a digital backlot set to be -- blue curtains and blue stage pieces everywhere. The date in the latest script has this revision occurring on July 14 -- a scant four days ago. On a nearby table, I see a pile of five printouts showing Ryan Church's concept art of this new location. They're all dated July 13. In these past four days, Gavin Bocquet's Art Department has whipped up a blue representation of the new set's contours, complete with fully detailed chairs featuring miniature monitors and control keys in the armrests.

In postproduction, this minimalist blue environment will become a Coruscant theater, with tiers of viewing boxes and an elaborate stage production yet to be determined.

That's what I'm on about a few younglings trying there best against bosk or IG88 or a young boba, but finally being cut down.

Perhaps chewie does have rebel sypathies, and even helps them out, then Han saves his life and he has to follow him around and that takes him on a more dubious path.  When they hook up with Liea and Luke before the battle of Yavin han is going to leave but chewie growls somthing and Han replie "I know what I'm doing" or something.  It's seems to me as if chewie still wants to stick around and help out.

if you go to http://search.w-k.net/cgi-bin/whois/whois.cgi? You can check who owns a domain title.  
Fallofthejedi.com
Revengeofthesith.com
Falloftherepublic.com
Riseoftheempire.com are all owned.  I suspect that all these have been brought by fans or companies looking to earn a bit of cash.  fallofthejedi and falloftherepublic are both owned by someone who looks like a fan, meaning that he’s either going to make some money, or knowing tight ol’ George, he’ll choose a different name. Revengeofthesith.com though is owned by a company called The Force Productions based in California.  Possible Lucus company? Check it out yourselves.  Anyone got any other pos titles that have been taken, there were lots of possibilities, i.e. alosthope.com that were not taken.  

This is fresh of hyperspace today, it should but this debate in the senate to rest.  "Tem is back, as one of the faces of the Republic clone troopers. Some of the soldiers are older, grizzled with Tem's face -- enhanced with battle scars, while others are more fresh-faced, played by Bodie Taylor. As Bodie did for Episode II's clone commissary scene, the actors film multiple takes of the same scene, in different positions, so that they can properly duplicated into large numbers. Since the clone trooper armor will continue to be computer-generated, Bodie and Tem wear blue bodysuits, lined with tracking markers to help gather performance data. "I just need their heads," says Rob Coleman.

If you haven't got hyperspace get it, it's worth it if you're a fan.

Christopher Lee said himself he was supprised how a couple of years had effected him.  He said he was not able to do any of the action scenes because he was too stiff.  So I reakon a space battle is going to be the only way to make him go out looking good.  Apparently his double does most of his work, so if there is a lightsabre fight it will be crap or shot from space so you can't tell who's fighting.  I'm sure he will get his sabre out but I reakon his going out in space!