Barack Obama was New Party member (far-left; Democratic Socialists of America?)
According to an October, 1996 page from the New Party (link) and a November, 1996 article from the editor of the Progressive Populist (Jim Cullen, link), Barack Obama was a member of the "New Party". The New Party is a now-defunct, left-leaning alternative to the Democrats and the Republicans that promoted "fusion voting" (newparty.org). It was started by Daniel Cantor (formerly with the 1998 Jesse Jackson campaign), Sandy Pope (union activist), and Joel Rogers (University of Wisconsin professor). According to this, in 1992 USA Today said they were "self-described [as] 'socialist democratic.'". They were involved with the SEIU and with ACORN; regarding the last, BHO is now lying about being linked to them.
While the New Party certainly appears to be quite far-left, the exact links between the NP and the Democratic Socialists of America (DSA), as outlined here, aren't exactly clear.
See also the many unverified-by-me claims made here; there are too many to list. However, if true, they provide a very clear, long-running link between Obama and the DSA.
UPDATE: See this and this for much more on the Obama-ACORN-New Party-DSA nexus. On a topic unrelated to CPUSA members, Marxists, etc. see this for a new-to-me topic: Obama's apparent friendship with Illinois State Treasurer Alexi Giannoulias, who was apparently involved in a sleazy financial scam.
Many of those discussing these "interesting" Obama links then close with, "when will the MSM cover this?" as if that means something. The MSM is not going to cover BHO's links if they can avoid it, and if they have to they're going to lie about them to the greatest extent possible. The only solution is to go out and ask Obama about the links at one of his public appearances. Get his response on video and upload it to a video sharing site. Let Drudge take care of the rest.
A spokesman for the Obama campaign insists his candidate ran as a Democrat in that race and said, "Don't believe the trash you read on the Internet."
Getting out our Clintonian parsing machine, does him running as a Dem preclude him being a New Party member? After all, fusion voting was what they were all about. Certainly someone must have access to contemporaneous records and other statements.
One other thing that's come to light is the photo here showing BHO with other NP members and endorsees; the caption is ambiguous, but they also say (without a photo) that Page 2 of that flier contains this:
New Party members won three other primaries this Spring in Chicago: Barack Obama (State Senate), Michael Chandler (Democratic Party Committee) and Patricia Martin (Cook County Judiciary)..."these victories prove that small 'd' democracy can work' said Obama
And, according to this, the New Party wasn't that radical at all. However, he bases that on what they later became, the Working Families Party. The latter group has since endorsed some Republicans.
UPDATE 3: From "New Ground 42/September - October, 1995" in the "Chicago New Party Update" section by Bruce Bentley (chicagodsa.org/ngarchive/ng42.html, also here):
About 50 activists attended the Chicago New Party membership meeting in July. The purpose of the meeting was to update members on local activities and to hear appeals for NP support from four potential political candidates. The NP is being very active in organization building and politics. There are 300 members in Chicago. In order to build an organizational and financial base the NP is sponsoring house parties... Candidates must be approved via a NP political committee. Once approved, candidates must sign a contract with the NP. The contract mandates that they must have a visible and active relationship with the NP... The political entourage included Alderman Michael Chandler, William Delgado, chief of staff for State Rep Miguel del Valle, and spokespersons for State Sen. Alice Palmer, Sonya Sanchez, chief of staff for State Sen. Jesse Garcia, who is running for State Rep in Garcia's District; and Barack Obama, chief of staff for State Sen. Alice Palmer. Obama is running for Palmer's vacant seat...
UPDATE 4: More here. According to that, the New Party was definitely on the left wing of the Democratic Party. It also discusses the 2002 book 'Spoiling for a Fight: Third-Party Politics in America' by Micah L. Sifry:
Sifry reports a quip by New Party co-founder, Daniel Cantor: "The shorthand strategy for accomplishing all this is to get the Bruce Springsteen, Lauryn Hill, and Pete Seeger vote united in one party." The Peter Seeger vote does sound like shorthand for the old-time socialist Left - but also for far-left-leaning baby boomers in general. Bruce Springsteen and Lauryn Hill point to young blacks and whites on the left, perhaps including, but not restricted to, openly socialist sympathizers. In short, the New Party was a mid-1990s effort to build a "progressive" coalition to the left of the Democratic party, uniting left-leaning baby boomers with minorities, relatively militant unionists, and "idealistic" young people... ...according to Sifry, the party explicitly thought of itself as made up of committed "progressives," rather than conventional "liberals."
UPDATE 5: There are pictures from their newsletters showing that BHO was a member of the NP here.