Some more great sigs I ran across in Slashdot:

1."I drank what?" - Socrates
2. Any sufficiently advanced technology is indistinguishable from a rigged demo.
3. Repeat after me, we are all individuals.
4. Lost: Pet sig. Insightful yet humorous. If found, call 555-5555.
5. 404 - Sig not found
6. No man's an island, unless he's had too much to drink and wets the bed.