We tried Masks of Nyarlathotep a couple of years ago, but found it was just too big and too long. We didn't go insane, the Keeper did

Last year we played the Curse of Cthulhu (IIRC Funghi from Yuggoth is the other name). Although the scenarios don't always link together well and the ending was poorly written, we had a real blast. It took a lot of my time Keepering it, but I had lots of fun. I used Photoshop and Indesign to create old parchments, withered clues, etc. The players loved it.
I can really recommend this campaign. The main campaign is six scenarios long (with two introductory scenarios) and is set all over the globe. Lots of fun!
Last Friday we finished the 'At the Mountains of Madness' campaign. It was a long while since I was an investigator again and this campaign is excellent. We finished it quite quickly (6 sessions I think). The only problem with the last part is that it's quite straight forward and players are bound to miss a lot. Once you've seen the main building, the end race is on. The story itself is terrific though...and facing off against a Shoggoth and losing 20 Sanity Points (jup, I rolled a '20' on a D20

) was hilarious.
For one-off scenarios I can really recommend 'The Crook'd Manse' scenario from the 'Mansions of Madness' book. It is a fantastic campaign for a onenighter or as introduction scenario for new players. It has all the right elements for a spooky night with cataclysmic ending. A real blast!