I considered Pieper, but didn't know where to put her besides Education, where Merkel is unlikely to renege on Schavan's appointment. Still, your point about this cabinet needing another Easterner is valid and gives me an idea... so here's my second take.
Chancellor: Angela Merkel (CDU)
Foreign Affairs: Wolfgang Gerhardt (FDP)
Interior: Günther Beckstein (CSU) (going with freivolk's objections, since the civil-libertarian wing of the "bürgerliches Lager" is weaker in 2005 than 2009)
Justice: Sabine Leutheusser-Schnarrenberger (FDP) (of course, the CSU's right wing in charge in Interior and the FDP's left wing in Justice is bound to give us some interesting intra-coalition discussions...)
Finance: Edmund Stoiber (CSU) (I thought to have Kirchhof as SoS, but that's not legally possible unless he enters the CDU and runs for Bundestag... hm.)
Economy: Guido Westerwelle (FDP) (Vice Chancellor)
Labour: Peter Müller (CDU)
Food&Agriculture: Gerda Hasselfeldt (CSU)
Defense: Wolfgang Schäuble (CDU)
Women and stuff: Ursula von der Leyen (CDU)
Health: Horst Seehofer (CSU)
Environment: Katherina Reiche (CDU) (ticks all the boxes, being an Eastern woman with a science background and bringing the ministries distribution to 8-4-4. Is also bound to be controversial since she is pro-nuclear-energy and pro-GMO.)
Education: Annette Schavan (CDU)
Foreign aid: Jürgen Koppelin (FDP)
Minister without portfolio and Chief of Staff: Thomas de Maizière (CDU)