Although many people believe that Samuel Johnson said "The
road to hell is paved with good intentions," he shouldn't get
credit for this one.
Johnson said something close,
but he was following in others' footsteps. In Boswell's Life
of Johnson, in an entry marked April 14, 1775, Boswell quotes
Johnson as saying (on some other occasion), "Hell is paved with
good intentions." Note, no prefatory "the road to..." Boswell's
editor, Malone, added a footnote indicating this is a 'proverbial
sentence,' and quoting an earlier 1651 source (yet still not in
the common wording).
Robert Wilson, in the newsgroup alt.quotations, provided two
other sources prior to Johnson. John Ray, in 1670, cited as a
proverb "Hell is paved with good intentions." Even earlier than
that, it's been attributed to Saint Bernard of Clairvaux
(1091-1153), as "Hell is full of good intentions or desires."
Just how it got to the road to Hell being paved this way,
and not Hell itself, I don't know.
For more of what Johnson is thought to have said, but
didn't, see the Apocrypha
For more of what he did say, see either the Sampler of Popular Quotes or the Topical Guide.