The centre-left Party of European Socialists is the next of the big two that's in with a chance of winning the European election. Their manifesto is also on their candidate's, Martin Schulz's, website. You can find the manifesto here (PDF). While the European Parliament has shifting coalitions from issue to issue (there may be a right-wing coalition on the economy one day, a left-wing one on civil liberties, for example), the centre-right EPP has been the biggest party in the Parliament for the last 5 years and has also been dominant in the Council and Commission. So the PES is approaching this election as the opposition, presenting itself as an alternative to the current political direction of the EU - hence the title of the manifesto: "Towards a New Europe".
On the economy, employment is the biggest issue for the PES, which says it has a long-term commitment to full employment. During the last Parliament it campaigned for a Youth Guarantee plan, and it pledges to increase its budget and extend it to everyone under 30. It wants a European industrial policy to support SMEs, and to increase protections for workers posted in other Member States by revising the Posting of Workers Directive. The PES wants decent minimum wages introduced across Europe through legislation or collective bargaining (the mix is probably a concession to the different national traditions - so I wonder how much this would translate into actual legislation or practical policy). As part of its idea of Social Union, the PES wants binding targets on employment, education and social cohesion.
Unsurprisingly, the PES condemns the "austerity-only" policy and wants more investments through national budgets. It's not clear if this simply means pushing for investment programmes to be a part of national budgets or if it should be something more co-ordinated. The PES wants the European Parliament to have a greater say in Eurozone economic and fiscal policy. When it comes to the financial sector, PES, which campaigned for a Financial Transaction Tax, says it will push for earlier implementation, bring in further regulations and create an independent and public European Credit Rating agency.
The PES reiterates its support for non-discrimination, integration and participation policies for immigration and asylum, and striking the right balance between privacy, security and freedom. However, there is little in the form of policy proposals here.
On the environment, the PES support further binding emissions targets and the use of Project Bonds to finance investments in renewable energy and technology. The PES wants to guarantee minimum access to energy for everyone in order to fight energy poverty.
The strongest themes of the PES manifestos are clearly in the areas of the economy and social justice, with some ideas on green policies. Justice and home affairs is its weakest point when it comes to proposals. If you want a more "social Europe" and support greater regulation of the financial sector, then the PES could be the party for you.