Since someone made a comment about Fire/Fighting being one of the only good combos for Fire, I decided to look up what Fire DOES pair with well (did this while avoiding homework). Note: I'm not a competitive battler, so I can't provide opinions from that standpoint. I'll start with the three we have. Sorry if this is a little long.
w = weak to, r = resists, i = immune to, * = both types weak/resistant to
Pure Fire: W: water, ground, rock. r: fire, grass, ice, bug, steel. i: none. Typhlosion.
Fire/Fighting: w: water, ground, flying, psychic. r: fire, grass, ice, bug*, dark, steel. i: none. Blaziken, Infernape, Emboar. Done 3 times, and the overall reason for this thread.
Fire/Flying: w: water, electric, rock*. r: fire, grass*, fighting, bug*, steel. i: ground. Charizard.
Now for some "new" stater type possibilities.
Fire/Water: Unless starters will suddenly start sharing the three main types with each other, this is unlikely, but anyway: w: electric, ground, rock. r: fire*, ice*, bug, steel*. i: none
Fire/Grass: like Fire/Water, unlikely that a starter will get another starters' type through evolving, but here it is anyway: W: poison, flying, rock. r: electric, grass*, steel. i: none.
More viable options.
Fire/Normal: Adds a fighting weakness and a ghost immunity. Otherwise, stays the same as pure Fire. Could be viable. I like it, anyway.
Fire/Electric: w: water, ground*, rock. r: fire, electric, grass, ice, flying, bug, steel*. i: none. The dual Ground weakness hurts, especially with how common Earthquake is, but that's the only weakness added. At least it could hit Waters back with STAB Electric moves.
Fire/Ice: w: fighting, ground, rock*. r: grass, ice*, bug. i: none. The large Stealth Rock weakness is the biggest problem here. Not that they're unwilling to have a starter face a large SR weakness (Charizard). At least it isn't hit by Hail . . .
Fire/Poison: w: water, ground*, psychic, rock. r: fire, grass*, ice, fighting, poison, bug*, steel. i: none, but immune to being inflicted with the Poison/Toxic condition. Duel Ground weakness doesn't look good, though.
Fire/Ground: w: water*, ground. r: fire, poison, bug, steel. i: electric. 4x Water weakness, but Stealth Rock weakness gets canceled out.
Fire/Psychic: w: water, ground, rock, ghost, dark. r: fire, grass, ice, fighting, psychic, steel. i: none. At least nothing doubles up . . .
Fire/Bug: w: water, flying, rock*. r: grass*, ice, fighting, bug, steel. i: none. Yeah, 4x rock again . . .
Fire/Rock: W: water*, fighting, ground*, rock. r: normal, fire*, ice, poison, flying, bug. i: none. This one doesn't look too good, 2 4x weaknesses and still weak to Rock.
Fire/Ghost: w: water, ground, rock, ghost, dark. r: fire, grass, ice, poison, bug*, steel. i: normal, fighting. Same weaknesses as Fire/Psychic, but at least it gets immunities.
Fire/Dragon: If they'd ever make a part-Dragon evolved starter, anyway. w: ground, rock, dragon. r: fire*, electric, grass*, bug, steel. i: none.
Fire/Dark: w: water, fighting, ground, rock. r: fire, grass, ice, ghost, dark, steel. i: psychic. Well, nothing doubles up in either weakness or resistance.
Fire/Steel: w: water, fighting, ground*. r: normal, grass* ice*, flying, psychic, bug*, ghost, dragon, dark, steel*. i: poison. While it has a 4x Ground weakness, the Stealth Rock weakness is canceled out (similar to Fire/Ground, just a different weakness magnified).
While Grass and Water have been pure-types the same amount as Fire/Fighting has appeared, I think F/F is more noticible because it's a dual type. There are some viable typings other than Fighting that don't look all that bad (I think Normal looks good, and maybe even electric, ground, steel, dark, and ghost). Once again, I don't battle competitively, so I don't know.
Personally, it doesn't bug me since I usually don't use the same starter type twice in a row for my first play through of a game, and I used Fire first recently, so I'll be picking a different starter. Just thought I'd throw this up for people who were curious.