PS (Socialist Party affiliated with PES): Have always struggle with achieving majorities in the parliament as no party to its left accepts to partner with it in government. Their previous leader and … was arrested preventively on suspicions of corruption and money laundry. Despite this and despite leading the country to financial calamity, the previous leader is still openly praised and admired by high rank officials within the party. That level of admiration only rivals with the hate by his opponents. His previous number 2, the popular mayor of Lisbon, leads the polls and is likely to be the next prime-minister.
PSD (Social-democrats affiliated with EPP): a mixed bag of conservatives, european liberals and socialists (some of whom defected from extreme left parties in the 80s). In 2011 the party won early elections after the previous government was forced to call the financial support of Troika. Due to the austerity measures imposed since, it has been an unpopular government likely to lose the upcoming elections.
CDS (Centrists, also affiliated with EPP): a party that combines social conservatives, social democrats and free-market liberals. Originally a centrist party has since moved back and forward between right and center. During one of those movements, his founder and historical leader defected to the Socialist party. Preferred partner of PSD in government.
CDU (Communists, affiliated with European United left): One of the last significant marxist-leninist parties in Europe. Has a strong presence in the south and industrial areas. Dominates the most active worker unions, specially the ones representing state workers. Its strong presence in the unions and local power makes it a dominant force in street demonstrations, giving it a stronger political power than its single digit election results would indicate. Has a historical conflict with PS.
BE (Left block, also affiliated with European United left): Union of left wing radicals. Founded by a charismatic university economics professor, it managed to become rapidly an important political force. With a bad sense of timing, the historical leader left at the time when similar parties were gaining importance in Southern European countries. The subsequent power struggle lead to the departure of some of its prominent figures to found new parties and political movements.
PDR (populist centrist party, likely to associate with ALDE): a one-man party, let by the populist previous leader of the lawyers bar association. After leading a small party to elect its first ever MEPs in the European elections, he left to found his own party.
LIVRE (affiliated with European Greens): The most well-known spin-off from BE. It differentiates itself from BE by assuming its willingness to form a government coalition with PS. Like BE, it mainly attracts upper-middle class urban voters.
Here are the results of the last poll: