A self-referential sentence is a sentence that describes itself in some manner. Classic examples; "This sentence is true" - or the derivation of Epiminides' paradox, "This sentence is false".

Another amusing example:

This sentence has three a's, two c's, two d's, nineteen e's, six f's, two g's, five h's, ten i's, two l's, twelve n's, nine o's, five r's, twenty six s's, sixteen t's, four u's, four v's, eight w's, four x's, and two y's.

Douglas Hofstadter presented some self-referential sentences in his book Metamagical Themas, but with an emphasis on numbers and how to "construct" them, such as this one;

In this sentence, the number of occurences of 0 is 1, of 1 is 11, of 2 is 2, of 3 is 1, of 4 is 1, of 5 is 1, of 6 is 1, of 7 is 1, of 8 is 1, and of 9 is 1.