Baptism doesn't require Holy Orders, so the "valid minister" of baptism is anyone at all. (A Catholic layman qualifies. A Presbyterian minister qualifies. In fact, there's a medieval council somewhere that decreed that anyone, "even a Jew" (their words) can validly baptize.)
The valid form requires the invocation of the Trinity ("Father, Son, and Holy Spirit", not "Creator, Redeemer, and Sanctifier" or drivel like that). Most conservative Protestants qualify there, too.
Valid matter involves water. There's been some questions raised about Protestants who baptize by sprinkling, but pouring and immersion are certainly okay. (Catholics do both.)
The intent can be a problem, but theologians generally agree that "intent" means "the intent to 'do what the Church does,' that is, to baptize in the name of the Trinity".
Protestant Eucharists, confirmations, ordinations, etc. are not recognized as valid because they require a valid minister. Protestant marriages are valid unless one or the other party is a Catholic marrying without a dispensation.
Thanks Campion. I was Baptized by full immersion in a little Baptist church in Utah. I was asked before becoming a Roman Catholic how I was Baptized. I do know that some Pentecostals (minority) do not Baptize using the Trinitarian formula as they believe the Trinity to be Pagan, those who follow the teachings of William Branham are an example.