Chalabi is a little bug, an opportunistic criminal in it soley for his own advancement. He left Iraq long before Saddam was any major figure and has a criminal conviction with a sentence to be carried out waiting for him in Jordan, for a serious bank embezzlement.
The strongest resistance to the Baathists at first was the Communists, later most resistance to their rule was from the Shia revolutionary party called al-Da'awa, as well as Kurdish nationalists/seperatists at most points. The Baathist coup was first engineered by the CIA to destroy the Iraqi Communist Party, and one of the main hobby's for the Baathists at first was collecting names from the CIA of ICP members to have killed.
There are 3 main communist parties in Iraq. One of which, the Stalinist Iraqi Communist Party (www.iraqcp.org), joined the quisling puppet council set up by the occupation officials. They have lost a great deal of support because of this hypocritical and opportunistic move.
There is another major leftist party, that I do like on the other hand, the Worker-Communist Party of Iraq. They opposed the invasion and occupation and remain independent, and it is geniunely looking out for the needs of Iraqi workers and providing a progressive avenue of non-violent resistance to the occupation. Currently they're involved in securing women's rights and maintaining the Union of the Unemployed, which has been attacked and harassed by the occupation forces for months (basically, the sort of strike-breaking treatment that they'd love to do over here). Their website can be viewed at--
http://www.wpiraq.org/english/Among the Kurds there are several small socialist/communist parties, but the Kurdish lands are mostly run by the Kurdistan Democratic Party and the Patriotic Union of Kurdistan, who imposed their control over most of south ("Iraqi") Kurdistan over time and run it with US backing as a proxy; other political parties in their regions must register with them to be considered legal.