Where to begin? It's thirty years later and people are still talking about Top Gun.
Heck, the film was one of the most popular films of the 80's, and the highest grossing film of 1986. It makes sense that people are still talking about it. It has so many memorable lines, so many memorable characters, that there was even a fleeting shout-out in Meet the Parents.
Somebody has even decided to arbitrarily establish one day out of the year to be Top Gun day (it's May 13th), where all you do is quote the movie for the entire day. Oh, and don't forget there's still a Top Gun store, just in case you want to wear a bomber jacket with patches you didn't earn. On top of this, you can also check out this priceless board on Pinterest.
While the realm of Top Gun fan sites isn't as developed and involved as those for, say, Lord of the Rings, there's plenty of stuff out there. There's this cool Top Gun wiki to help you get to know the characters and, oh, every detail you could possibly imagine.
On top of that, there's a whole lot of fan fiction, in which fans make up their own stories using Top Gun's characters. In addition, there are all sorts of Top Gun swag available for purchase on Amazon and just about everywhere else. It even seems like people need to mention Top Gun whenever they talk about something remotely related to the film (Navy pilots, F-14's, aircraft carriers, and the like), as you can see here.