TV News Show Transcripts: The sources I have found useful for TV news show transcripts are:
Fulltext Sources Online - a great source for locating transcripts.
The web site for the show and/or the network. I generally find these using Google or another good search engine. PBS and CNN both post transcripts.
Broad transcripts databases are available for many shows on Lexis Lexis (NEWS;SCRIPT) and Westlaw (TRANSCRIPTS). There are also narrower databases. For example, Lexis offers a database of general TV and radio news transcripts (EXEC;SCRIPT), another for legislative news and Congressional hearings (LEGIS;SCRIPT) and political campaign news (CMPGN;SCRIPT).
Transcripts.TV sells transcripts of ABC news shows including 20/20, Nightline and World News Tonight.
Burelle's Information Service, which also sells transcripts.
FDCH, a transcription service, will tells you who to call to buy their transcripts for different news shows.
The Broadcast News Transcript & Video Sources page posted by the Ohio University library.
TV News Show Recordings: Sources for video of TV news shows include:
TV News Search & Borrow;
YouTube, if you're feeling lucky;
The web site for the show or network;
Vanderbilt University's Television News Archive, which posts Web summaries of all network evening news shows, plus many special reports (etc.). If you want to see a show described in a summary, you can borrow the videotape from Vanderbilt;
A commercial vendor such as Critical Mention;
The Broadcast News Transcript & Video Sources page posted by the Ohio University library;
You might also want to contact the Paley Center for Media (formerly the Museum of Radio and Television). The Center's lets bona fide researchers view programs from the Museum's collection in their on-site Scholars' Rooms in LA and New York City.
Radio News Show Transcripts & Recordings: Sources for radio news transcripts and recordings include:
The web site for the show or network (e.g., NPR);
Burelle's Information Service, which has National Public Radio and others;
You might also want to contact the Paley Center for Media (formerly the Museum of Radio and Television), located in New York City and Los Angeles. The Museum lets bona fide researchers view programs from the Museum's collection in their on-site Scholars' Rooms.
Monitoring: See the "Monitoring Services" section of the Television & Radio entry.