Politico reports that Chris Suprun, one of Texas' 38 Republican electors, has indicated that if Donald Trump wins his state, as seems likely, he may cast his electoral college vote elsewhere. Earlier in August, Baoky Vu, then a Georgia elector, indicated the same, while going even further by saying he wouldn't vote for Trump in November. Shortly after those comments, Vu resigned.
About half the states bind electors legally, the remainder do not. Texas and Georgia are two of the states that do not require electors to vote in line with the popular vote results. Electors not voting as pledged are known as 'faithless electors'. These are rare, particularly in modern times, as the electoral slates are usually comprised of those very loyal to the party they represent. Wikipedia has a list of faithless electors.
When a voter goes to the polls on November 8th, his or her vote for a presidential candidate is actually a vote cast for a slate of electors selected to represent that candidate/party in the electoral college. There is a separate set of electors for each party on the ballot. Independent and write-in candidates may or may not have a slate, it seems to vary by state. The number of electors in each slate are equal to the state's electoral votes.
Electors are listed on a on a Certificate of Ascertainment, which each state is required to file after the election. Here's the Texas one from 2012.
The electors associated with the winning candidate in each state will meet to vote on December 19th, where each will individually cast his or her electoral college vote. The votes are recorded on a Certificate of Vote, a copy of which is sent to the President of the Senate (VP Joe Biden) for the official count on January 6, 2017. Here's Texas' Certificate of Vote from 2012.
If Mr. Suprun, or another elector, were to cast their vote differently than as pledged, it would occur at this December 19th meeting.