Thanks to Scrafty, I love Dark/Fighting! It's a combination that counters some of Fighting's weaknesses; Dark deals with Fighting's inability to hit Ghost-types and deals with Psychic-types. Fighting also allows for more offensive coverage too.
My other favourites are Dark/Dragon (two favourite types), Dragon/Fighting, Fighting/Flying, Dragon/Ghost, Steel/Flying, and Dark/Flying.
Now I'm waiting for Ground/Fighting, Ghost/Normal, and Steel/Poison.