I and a friend spend random lunch hours hashing out ideas for SCPs, though I've never submitted a successful one (until now, hopefully) and I don't think she's ever submitted one at all.
The ideas we've had and developed jointly, or that I've bounced off her, are thus:
1. Time Pit/Space Pit - Her version is Time Pit, a gravel pit about thirty feet deep where the flow of time slows exponentially as you approach the bottom. Someone who fell into the pit would see everyone outside begin to move exponentially faster, and would see Armageddon when they finished. My version is Space Pit, a pit that goes down thirty feet from the outside and an infinite distance inside. The further you fall, the more space is stretched, and the flatter you seem to outside observers. Time is unaffected, though the pit has technically-infinite distance. Digging up through the bottom of the Space Pit has been done, it's about thirty feet down from the outside, the effects don't extend outside the walls of the pit, and it's just a regular pit about six feet to a side from the bottom, with no visible light source. Efforts have begun to build a staircase to reach the surface, carved into the pit walls. Digging through the walls of the Space Pit, or any part of the Time Pit, is impossible.
2. Alchemy - Idea I had recently. Brass chamber, about six feet tall and three feet across, no decorations, two levers on one side and a whole mess of pipes opposite the hatch that lead to four boxes. One lever is labelled "Ανάλυση" and the other is labelled "συναθροίζω." Pulling the first lever with something in the chamber causes the object to vanish and the boxes to fill with various amounts of the four 'old' elements, namely air, water, sulphur, and sand. Pulling the second lever with any amount of the four in the boxes causes a seemingly-random object to appear in the chamber.
3. [Anti-Music Man], an unfinished project I've been working on sporadically for the past year. Also, pretty much anything else in there.
Thoughts? Critiques? Suggestions for improvement? Any and all would be welcome.