I believe this first appeared in Hofstadter's Metamagical Themas. Fill in the blanks below with numbers that would make the following sentence true:
The number of 0s in this sentence is _, of 1s is _, of 2s is _, of 3s is _, of 4s is _, of 5s is _, of 6s is _, of 7s is _, of 8s is _, and of 9s is _.
There are two solutions. Enjoy :)
Update: As dws points out, I meant numeric numbers, as in non-zero-padded positive integers, or /^[1-9]\d*$/ for the regexpically inclined. I'll leave it to dws to enumerate the remainder of the class of solutions for which words are permissable in the answer. :p
s aamecha.s a..a\u$&owag.print