EMNID puts out what is called the Sunday-Question

(Sonntagsfrage)
http://www.wahlrecht.de/umfragen/emnid.htm
Take a look at the values.
The CDU is generally about 14 points ahead of the SPD. It has been hanging steadily at around 40-42%.
The SPD has sunk from 28 to 24 since January.
The Greens are hanging in at around 12%. This is actually better than in past years.
The FDP at between 5-6%.
Right now, if these values absolutely hold, then neither CDU/FDP nor SPD/Greens will be able to build a coalition.
Who is the Pirate-Party (Die Piraten)? Well, in a sort of way, I am tempted to call them the Tea Party of Germany. The are stirring up all kinds of trouble in many towns and cities, encouraging recall elections of issues (called Bürgerbegehren or Bürgerbescheid), they are especially hostile to the arts in any way. The Pirate party is just under the 5% hurdle, I don't believe they are likely to get there, but it could happen.
Which leaves us with the Linkies - the extreme-left, the old worn out communists from the past who are now calling themselves socialists, holding at 8%.
So, let's do the numbers, assuming that the election would be exactly as this current poll is showing, just for demostration purposes:
CDU (CSU) 40 / FDP 6 = 46 - not enough.
SPD 24 / Grüne 12 = 36 - definitely not enough
SPD 24 / Grüne 12 / Linke 8 = 44 - not enough
CDU (CSU) 40 / FDP 6 / Greens 12 = 58 - possible coalition
CDU (CSU) 40 / SPD 24 (Grand Coalition) = 64, a strong possibility, just as in 2005.