What are your favorite credits / "thanks for playing" / bookend maps?

BTSX E1 and E2 ending levels. It's something that strikes my soul in a way, which i usually don't expect from doom levels.
 

I too love the ones already mentioned here, I really love Tangerine Nightmare's ending, the path showing credits for all the mappers was pretty cool

Axolotl has a cute spoof of Ribbiks' website in the final slot:

The ending of Wormwood which later gets revealed in its true form in the sequel

The ending of Auger;;Zenith

Map 30 of Ancient Aliens. You'll know why:)

I really like the ending map from the recent DBP50, which doubles as both credits and epilogue, revisiting scenes from the other maps while adding a bit of heartwarming story text to wrap things up.

I was toying with the idea of a map that has Underhalls opening vista but once you go closer to 3 zombiemen, the walls lower and you hear alert sound of 12 cyberdemons, but probably it will not happen as I don't have even time for creating / finishing regular maps, so I am just writing this silly post.

Arrival's ending map is quite an experience - a sense of quiet after a series of long and tough battles, almost giving a sense of loneliness.

Heartland's 'Arrhythmia' will always have a special place in my heart - the beat, the endless corridors, the music restarting, the end...

I really like Going Down's map 30. At first it just seems like a no monster "thanks for playing!" type of map, but if you explore the apartment a bit, you end up triggering a surprise. The whole WAD is quirky like that, and the final map just solidifies that. 

You ever read the title and waltz in to post something, only to find it's already the very first screenshot in the thread?

That is the canonical ending to the Doom saga right there - bravo, @antares031.

Hellcore 2.0 had an interesting credits map which used various parts from unfinished levels and introduced a new enemy. It's also worth playing just for the midi track alone.

My favorite recent end map is the one in Fractured Worlds. It's a beautiful scene with two layers of lore, one peaceful and mournful, the other deeply disturbing. The contrast is complex and probably unfathomable, but I interpret it loosely as: "You are dead and your spirit is left to haunt its final resting place, and now you have glimpsed the horrors that lie beyond human comprehension; but the battle has passed on to other people, and the weight is off your shoulders, though maybe you can help them somehow."

Better still, it has an alternate ending as a reward for having passed through all the secret quests in map 06 and bypassed the death exit.

Shout-outs to both Team Rocket credits maps; the Marian drawings are my favorite part.