Each state determines their own elector laws, and the Supreme Court said that's fine. They all have the popular vote determine which slate of electors will vote in the Electoral College, in the manner perotista wrote. What happens to faithless electors can be nothing, a fine, or instant replacement with a backup elector. I don't think any states specify jail sentences.

There are 33 states (plus the District of Columbia) that require electors to vote for a pledged candidate. Most of those states (16 plus DC) nonetheless do not provide for any penalty or any mechanism to prevent the deviant vote from counting as cast. Five states provide a penalty of some sort for a deviant vote, and 14 states provide for the vote to be canceled and the elector replaced (two states do both).