Clinton and Obama are the most moderate candidates from the Democratic field. Kucinich is actually liberal, by which I mean his platform is basically indistinguishable from FDR's (which, these days, gets you called an extremist). Edwards was a recent liberal convert (just like Romney was a recent conservative convert). Dodd? Liberal. Gravel? Liberal. Richardson was the only other quasi-moderate.
Clinton and Obama only look liberal because the neo-cons have dragged political discourse so far to the right over the last 25 years.