Some lists I like:
- Most Commonly Used Passwords — Stick that in a local database and clean against your users logging into your site.
- Airport Code Country Airport
- HTML Tag List — Nice if you're building some kind of HTML parsing script and need a list.
- Chinese Zodiac — Again, what I built this site for. If someone needs a list, here it is in a myriad of formats.
- Words Containing The Letter X — So good.
- Common XSS Vectors — Eep.