General rule of thumb is GOTY editions of games have some sort of content that wasnt included in the initial launch of the game (like Fallout and the extra content or Gears and the map packs), greatest hits editions of the games are normally re-packaged and much cheaper but are the same as the original launch of the game , like Uncharted greatest hits doesnt come with anything different than it did day one.

The only semi-exception is when it comes to Special/Limited editions of games. They usually have something extra and usually it is in the form of content outside of the game like Making Of's and art books/soundtracks and such. It's rare when you get in game content that others wont have access to at some point. Another new approach is giving the people who buy these editions something in game that usually takes a while to get. It's a crapshoot, sometimes you get some really cool extras (like the Fallout 3 special edition or Batman Arkham Assylum's batarang) or you get some lame stuff (like the street fighter 4 lame anime and download coupon for extra costumes.)

Greatest Hits = Usually nothing extra
Game of the Year Edition = Usually some content that was released after initial release
Special Edition = Usually for fans of the series with extra content that normally doesn't effect gameplay too much
Usually wikipedia will have some blurb on there if there are different versions of the game and they usually say if a particular title has reached "Greatest Hits" status.