Examples of type 1 (characters involved in production)
The Cheat of Homestar Runner stars in a parody of G.I. Joe called Cheat Commandos. Also, another character, Stinkoman, has his own anime series.
The Strong Bad E-Mails is also a type of show, with Strong Bad giving it a changing opening theme and referring to it as his "E-Mail Show." Also there was The King of Town's Very Own Quite Popular Cartoon Show.
Homestar Runner also has Teen Girl Squad, an "indie comic" about four "teenage girls between the ages of 13 and 19" dying in humorous ways, crudely drawn and voiced by Strong Bad.
4 Gregs is a comic drawn by the titular squad. Who in turn were in a comic drawn by the Gregs. Who again were drawn by the girls. And so on. This gets so meta that even Strong Bad loses track.
Episode 77 of Bonus Stage has Joel and Phil optioned by G4 to create their own cartoon for the network. The show is unfortunately ruined by Phil's endless suggestions. Much of the episode is a Take That to G4.
Two back-to-back episodes of GEOWeasel feature shows starring the main characters. The first features The Nar Show, which Nar wins in a contest (the flier for which says, "millions will enter, 2.5 will win") and Weas tries at every turn to stop. The second is a dating game that is meant to introduce only one female character to the show.