Elphaba: Willemijn Verkaik (source: her website)
Elphaba alt.: Roberta Valentini (source: her agency)
Glinda: Joana Fee Würz* (source: her agency and her website)
Glinda alt.: Valerie Link (this used to be on her official website but they took it down, presumably because no official announcement has been given yet. Valerie has however confirmed she was going.)
Fiyero: Mathias Edenborn (NOT OFFICIAL, told by him at the stagedoor)
Mme Morrible/Akaber: Barbara Raunegger (NOT OFFICIAL, stagedoor info)
Boq/Moq: ?
The Wizard/Der Zauberer: ?
Dr. Dillamond/Dillamonth: ?
Ensemble:
Bero Antunovic (swing, Fiyero u/s) !until May!
Helena Blöcker (Morrible u/s)
Christina Maria Brenner* (Morrible u/s) (source: European Musical Academy)
Vanessa Campbell
Heather Carino (currently swing)
Ben Cox (currently swing)
Melanie Gebhard (Elphaba u/s) (source: her website)
Rhys George (currently swing)
Kit Gresty
David Hardenberg* (source: his bio on a Dutch musical theatre's website)
Matt Jones* (Chistery)
Katrin Löbbert (currently swing and Glinda u/s)
Theano Makariou (currently Witch's Mother)
Carly Meyers*
Dashi Mitchell*
Janna Yngwe* (Nessa u/s) (source: Guildford School of Acting)
Carl van Wegberg* (swing, Fiyero u/s) (source: his fanclub) !from May!
* haven't done Wicked in Germany before.
Current members who have confirmed they were NOT going:
Lucy Scherer (Glinda)
Stephan Luethy (Boq)
Andrea Casati (ensemble, Boq u/s)
Stefan Poslovski (Witch's Father, Wizard and Dillamond u/s)
Barbara Schmid (swing)
Filippo Strocchi (ensemble, Fiyero u/s)
Maria Walter (ensemble, Elphaba u/s)
+
Jessica Lantto (ensemble, Morrible u/s), who hasn't actually said anything, but she left at cast change in Feb 2009 and returned only because Juliana de Aquino passed away. Since both ensemble + Morrible u/s positions have been taken, I think it's safe to assume she will not be going to Oberhausen.
Ensemble info is purely from the people themselves since most of them don't have an official website.
And some extra info.
Lucy Scherer will be playing Sarah in Tanz der Vampire in Stuttgart from the opening night until March 28, 2010. After that she's doing Lulu: das Musical in Innsbruck (Austria), a musical about one of Jack the Ripper's victims (don't ask
Roberta Valentini will be doing a solo show in Munich (Germany) in February, Verlangen wir denn zuviel? and a special one-night-only performance with Leigh Martha Klinger on Valentine's Day. Source: Off-Broadway Musical Theatre in Munich
Maria Walter will be doing Tarzan in Hamburg. Not exactly sure as to when she's starting.

