I knew this existed, but I was too lazy to look it up, and then Cleolinda did the work for me by providing links right on her Twitter feed: Twilight in 15 minutes. She actually linked to the new one (Eclipse in 15 Minutes), of course, but there were helpful links right there to the others, so I'm golden. And it is, as usual, very funny.
If you've never read any of Cleolinda's parodies, she's been posting them on Livejournal for years, and she even has a book, which has completely different parodies than the LJ ones, although it's now out of print (but I'll post an Amazon link anyway). (She also writes this almost unexplainable thing called The Secret Life of Dolls which I totally adore, and wish she would write more of. Cleolinda is totally to blame for me ever deciding to watch Twilight in the first place.)
Added: At my husband's suggestion, we checked out one more piece of Twilight mockery after I wrote this: Rifftrax, from the Mystery Science Theater guys. It's downloadable audio which you then synch up with the video - the effect is like MST3K minus the robot silhouettes. It was the first time we'd tried it but it worked quite well. For $3.99, it was a fun bit of entertainment.