There's no point in me repeating the role that Germany had in the origins of the First World War, as it's been clarified pretty well in the rest of this thread.
But Russia, Austria-Hungary and Serbia all played their parts.
Russia in particular had a point to prove. Having lost the Russo-Japanese War to a nation that was, at the time, viewed as a third world country was humiliating. Furthermore, the Bosnian Crisis and the Russian inability to continue her support of Serbia when threatened by Germany in turn threatened Russia's position as a 'Great Power.' And in the wake of massive defence spending and an increase in the size of the Army, Russia found herself in a position in 1914 to be able to back her political stance with military power.
In terms of Austria-Hungary, she was a power in decline. There was a very real threat of A-H replacing the Ottoman Empire as the 'sick man' of Europe, so backing down to the tiny nation that was Serbia in the wake of the assassination of Franz Ferdinand was unthinkable. A-H, similar to Russia, wanted to reaffirm her position as a Great Power. A-H had also had previous problems with Serbia such as the Pig War and the fact that Serbia opposed the annexation of Bosnia. As such, the issuing of the July Ultimatum to Serbia was as much solving the 'Serbian Problem' as it was revenge for Franz Ferdinand's death.
Serbia, on the other hand, was a firm advocate of Pan-Slavism and thus believed that Bosnia, as another Slav nation, should be under Serbian control, putting them at direct opposition to A-H during the Bosnian Crisis. Additionally, allowing A-H to annex Bosnia increased the Serbian fear that they would also become a protectorate nation.
So in regards to Serbia, A-H and Russia there were other underlying factors that contributed to their decision to go to war. Furthermore, none of Europe's Great Powers knew how a conflict that originated in the Balkans would pan out. The majority thought that the conflict would remain localised, hence the lack of any real attempt to solve the 1914 crisis. Subsequently, the Alliance system meant that each Great Power was dragged into conflict and meant that by the time war was declared, anything that France and Britain did could only be reactive rather than preventative.
So, to answer the OP's question, Germany must take it's fair share of the blame for the outbreak of World War One but there are plenty of other nations plus a few unfortunate factors that also contributed.