I've come up with a few ideas as of late, and I figure I'd share them with you all to see if they're even worth effort.
1. A phonograph that plays only one record-an instrumental piece that listeners can't give lyrics to, no matter how hard they try. When any form of music with lyrics is brought near it while it plays, the lyrics are removed permanently from the song. If that copy of the song is played, all that is heard is the instrumental version. This idea isn't my favorite, being it is a "X that does Y when Z."
2. A giant, invisible, untraceable cat that will randomly appear at crowded, public events. There are thousands of witnesses who see it, but the cat technically doesn't exist. I oddly like this one, being it's short and simple.
3. A man who has every drug known to man, and several more, flowing in his bloodstream. He isn't harmed by it physically, actually, he's rendered immune to a good amount of disease, but is essentially addicted to every drug in him. Due to his addiction to his own blood, he refuses to give samples to Foundation staff willingly and has to be sedated and restrained to receive samples. My only apprehension is the fact that this would be a humanoid SCP, something that requires plenty of skill.
4. A mirror which literally reflects whatever it shows. For example, if it is placed in front of a column and hung on a blank wall, it will reflect the column and make a hole in the wall leading to a room with just the column. Admittedly, very similar to SCP-093.
Finally, I do have one idea written up-http://scpsandboxwiki.wikidot.com/catboy637. A "possessed" chimney.
If anybody thinks they could take these ideas and improve upon them, please feel free to. Just let me know first. Thanks in advance.