AMV Hell/Funny

What really happened to the Titanic.
Bohemian Rhapsody + Star Trek + Outlaw Star = Absolute Hilarity
You cannot forget the brief but hilarious Vegeta channeling Whitney Houston.
Frieza singing The Memory Remains while beating the shit out of Goku. The fact that the part he was singing was sung by an old woman only made it 110% funnier.
Inspector Zenigata and Lupin III taking the place of Dora the Explorer and Swiper, respectively.

Suddenly, Paprika makes so much sense.
A blink-and-you'll miss it scene from AMV Hell 5 toes the line between hilarious and little disturbing.
No link to an individual clip, but in AMV Hell 5 there's a blink-and-you'll-miss-it scene from Naruto where a ninja sinks into a puddle... with the sound bit "I'M MELTIIIIING!" in the background. Hilarious, because if you get it you are probably one of the five people who remember what game that's from without looking at the credits.
Just the sheer passion mixed in with this little ditty using Clannad is hilarious.
Light goes off on Ryuk's latest idea.
The Ginyu Force mashed up with Robin Hood: Men in Tights calls for hilarity.
Bleach and Girl Directions gives epic chortles.

This scene from AMV Hell 0.
Gendo as Psycho Dad from 0. Always a laugh riot.
0's Infamous CORN! scene (Oh so very NSFW),
- It's not different at all, is it Steve? Ahahahahahahahahahahaha!

That part in I think it was AMV Hell 4 where the famous lines from Troll 2 (They're eating her! etc.) actually fit on one of the holy-crap-I-think-I-just-wet-myself scariest scenes of Neon Genesis Evangelion. The scene? The mass-produced EVAs are ripping apart EVA Unit-02. Cut to Shinji, screaming THEY'RE EATING HER! AND THEN THEY'RE GOING TO EAT ME! OH MY GOOOOOOOOD!
Negi Springfield indeed has got the magic stick.
If unofficial ones count, AMV Heck has a brilliant rendition of the infamous toothpick scene from Neon Genesis Evangelion set to the Doo Wop's "Peanut Butter Song".
Lucky Styrannosaurus Rex.