Here’s a useful link: The New York Times provides a nutshell summary of what the Presidental Candidates’ health care plans are, and how (they say) they’ll pay for it.
Kucinich is (predictably) the only candidate offering true, universal, single-payer health care. But although that’s the best plan, I doubt it’s politically possible to go there in a single step. In particular, voters who are satisfied with their current health care coverage — that means most of them — are extremely vulnerable to “booga-booga! The Democrats are going to take away your choice!” attacks by Republicans, unless the Democrats can honestly say “if you like what you have now, then you can keep it.” That’s the big advantage of the Clinton/Obama/Edwards/etc plans.