Freddy vs. Jason/WMG

Freddy and Jason live on
Jason decided to return to camp crystal lake and started all over, but decided to keep Freddy's head. Freddy was able to find a new head which was less ugly, but had worse burns and a new arm. Freddy built a new glove, since his old one was at the bottom of the lake, which was slightly different and he went right back to Elm Street
 * Take note - when Freddy and Jason were fighting in the camp, it wasn't the old, trashed one - it was being rebuilt. Again. You know, because Jason had been dead for a while and people are idiots. That was one helluva setup for more Camp Crystal Lake slaughter.

Jason's in a coma at the bottom of the lake and Freddy's stuck in his mind
Jason can come back for Jason X, but Freddy was unpleasantly surprised to find that nobody alive remembered him and Jason doesn't sleep much. Freddy's in a very nasty situation...

The end credits were part of the film's story.
It was a long POV shot from Freddy's perspective. The background was the floor of Jason's house, the dripping blood came from Freddy's severed head as Jason carried it around looking for a place to put it. The blood-loss caused Freddy to hallucinate the credits and the song was Freddy singing to Jason to try to convince him not to use his head as a flower pot.

This is the true end for Freddy
At the end of the movie Jason stuck Freddy's head on his knick-knack shelf. Freddy is thus stuck in limbo; he's not dead so he can't re-enter the dream state, but he's just a severed head so he can't escape Jason's cabin either. He's doomed to sit up there next to Jason's bobble-heads until the end of time.
 * Whatever the final scene of Fvs J suggests, Freddy will be going back to Springwood to slaughter more kids. He succeeded in spreading the fear he'd wished to when Will & Mark told the Legend of Krueger at Springwood High so there are tons and tons of high schoolers who know Freddy now. Freddy may have lost the battle, but he won the war.
 * One way or another, you're right about it being the end of [that incarnation of] Freddy. When a (gratingly unnecessary) remake starts a new series in Hollywood, the old series is automatically kaput. So if there are any more sequels they will be to the NOES and F13 remakes.
 * Wasn't there a comic sequel called Freddy vs Jason vs Ash that continued the story?
 * The 6th Elm Street film also theoretically takes place in the future ("Ten years from now"), like Jason X. If that hasn't happened yet, it would explain why Springwood is a more-or-less normal town in this film, but a nearly empty ghost town with no children and the remaining adults completely insane in Freddy's Dead. No way the town could have been repopulated and Freddy's existence suppressed so well. Even if you assume that the time given in the beginning was ten years from the release of that film (1991), then since this film takes place in 2003 they would have had to fix the town in a mere two years.
 * Then maybe Freddy succeeded in this film after all. He will indeed get credit for all the killing Jason did, and that is what will give him enough power to bring about the events of Freddy's Dead.
 * The promotional materials state that this film takes place exactly 4 years after Freddy's Dead. The writers just chose to ignore the "10 Years From Now " thing just be pragmatic.
 * Footage from Freddy's Dead is seen in the opening prologue, showing that those events have already happened.

The whole movie is part of a conspiracy
On the part of Pinhead, the lead Cenobite. Even if he doesn't live in hell proper, it's not outside the realm of possibility that he can freely travel to dimensions that aren't Earth. Over the course of the movies, he's occasionally succumbed to the urge to hurt people just for the sake of it. Tricking people into opening the box is too much work, but feeding a predictable spirit like Freddy the idea of using Jason wouldn't be any trouble at all. He gets to inflict a little more of the suffering that isn't technically in his job description, and then watch to creatures that he more than likely loathed beat the stuffing out of each other.

The movie is set in 2004 or 2005.
If we assume that the first movie of "A Nightmare on Elm Street" is set in 1984, then the second film is set in 1989, the third is set in 1990, the fourth and fifth are set in 1990 or 1991, "The final Nightmare" is set in 2000 or 2001. And this film is set four years later of "The Final Nightmare".
 * A Nightmare on Elm Street takes place in 1981, not 1984. The tombstones of Kristen and Kincaid in Nightmare 4 show their death date as 1988. Nightmare 5 opens with the high schoolers graduating and a "Class of '89" banner. Working backwards from those dates places the events of Nightmare 1 in 1981. Freddy vs. Jason features a "Coming in 2004" sign on the construction at Crystal Lake, setting it in 2003. According to the "four years" thing, Freddy's Dead would then take place in 1999.