I read these bumpersticker ideas on the The Dilbert Blog today. (Have I already mentioned to you that it's my new favorite weblog? Oh I have? Oh, okay.)
Meditate on these:
"The sentence below is true.
The sentence above is false."
"If you try to fail and you succeed, which have you done?"
Also, someone brought up some old Jack Handey sayings. I like this one:
"If you ever teach a yodeling class, probably the hardest thing is to keep the students from just trying to yodel right off. You see, we build to that."
(I'm too lazy today to come up with my own ideas.)
UPDATE (10 p.m.): Remember those Magic Eye pictures we all stared at in the late 80s? The first puzzle above reminds me of them in that I just had to let my brain relax for it to make sense. I think I can sleep now.