Upvote:4
The MyTSA App has some of this information, though it's crowdsourced (plus some historical "how busy is it likely to be" data), and may be basically useless given a lack of reported results.
There are a few airports that collect wait time data themselves and report it to passengers, including Dulles (Washington DC) (the information is supposedly online in addition to the airport signage, but I have no clue where), Houston Intercontinental (see "Security Checkpoint"), and Atlanta.