I'm not sure if we're allowed to link to the old forum or not (and I can provide a direct link if we can), but Kensuke kindly made a updated version to DonkeyPunchJr's guide, which is an excellent quick reference if you're looking for ideas.
Kensuke's original post:
I thought it would be fun to write a small guide to compliment this one from GFaqs a lot of people here seem to be using. That guide is a bit older now and since then new amazing combinations have been found (mainly Shikari/Red Mage). I put most combinations under characters so you can mix and match your party more easily.
Vaan – Can pull off any job thanks to high stats everywhere. A lot of people like him as Shikari though for 'canon' reasons.
Shikari/Foebreaker – DPS (genji gloves) + Breaks. Big con is that it has no magic (therefore suits Bash and Balthier better).
Shikari/White Mage – Nearly invincible tank with healing.
Shikari/Red Mage – Tank+Black Magic+support spells. Jack of all trades and mostly great at them all (makes for an amazing 'leader character'). Penelo and Ashe are also great with this one.
Pretty much any job combination (can use any of the ones below)
Balthier – Best as a katana user, but a lot of people like him as Machinist.
Machinist/White Mage – Healer/support that uses gun on downtime (better used by others because Balthier isn't a great mage).
Machinist/Uhlan – Gunner that can hit all weaknesses and is able to dish out big damage.
Shikari/Foebreaker – See Vaan list above.
Bushi job (see below).
Basch – Best as a katana user, but a lot of people like him as Uhlan (he's fastest with spears too).
Uhlan/Archer – Can use both jobs very effectively, gives a ranged option + use of many item lores.
Shikari/Foebreaker – See Vaan list above.
Bushi job (see below)
Ashe – Has the best magic stat in the game, but can also work with physical jobs because she also has decent strength.
Knight/Time Mage – Healing (with espers) + Time Magic + decent damage. Makes good use of her stats.
Uhlan/Time Mage – Decent with spears and can use that time magic effectively.
Ashe/Penelo can both do these jobs very well. Fran can do them too, but not as great.
Black Mage/Monk – All HP lores making your Mage tanky + ultimate Holy spell. Only con is that the 16 battle lores Monk has mostly go to waste.
Black Mage/Archer – Access to all item lores for emergency support + some extra HP lores.
Black Mage/Machinist – Same benefits as archer with a few less item lores. Access to some late game time magic.
White Mage/Time Mage – Ultimate support character, but perhaps not enough gambit slots to use it efficiently.
Black Mage/Red Mage – Ultimate Ardor (fire) spell, but a lot of overlap and only 2 swiftness.
Fran – Probably best as a damage dealer with poles (she's the fastest with that weapon), but a lot of people like her as a Red Mage and Archer for canon reasons.
Red Mage/Archer – Good utility for most of the game and an endgame combo with burning bow+ardor.
Red Mage/Machinist – Effective user of measures, allowing for amazing evasion. Access to Dark Shot + Black Robe combo.
Monk/Foebreaker – Allows you to use Kanya+Genji Gloves, nearly as strong as the Bushi alternative (you can have both though).
Bushi gets the strongest weapon in the game (Kumbha), which makes it the best DPS class. There are lots of useful combinations with it. All of them are best used with Bash, Balthier and Vaan. Ashe can do well too with the ones that use magic.
Bushi/Knight – Allows the Bushi to use some healing spells. Heavy Armor + 10 battle lores. Access to strong Excalibur combo.
Bushi/Uhlan – Very strong in terms of DPS because of Heavy Armor + 13 battle lores.
Bushi/Monk – The strongest one with in terms of DPS with 16 battle lores and access to Heavy Armors through an Esper. Allows Bushi to use Curaja + great support spells.
Bushi/Foebreaker – Breaks of course, but also Heavy Armor + 12 battle lores.
Bushi/Shikari – Ultimate Yiazmat killer, but besides that not as great.
Whatever you pick, another thing to keep in mind is that you get two Genji Gloves in this game. That's the equipment that allows you to do combo attacks for insane physical damage in the endgame. Only Bushi, Knight and Foebreaker have access to the Genji license. Besides that you want a weapon with a good combo rate. Kumbha (katana) is the best one for that, followed closely by Kanya (pole). Vrscika (hammer) and Mesa (ninja blade) are also good. It's just something to keep in mind while dividing up jobs. Monk for example could use a subjob with a genji license to use the Kanya efficiently.
There are a lot of other decent combinations, but I just tried to focus of some of the better ones. Keep in mind you can finish the endgame with literally any combination and that you should pick whatever you think would be fun. Still, here are some combinations with bad synergy you should probably avoid: Machinist/Archer, Machinist/Time Mage, Samurai/White Mage, Black Mage/White Mage, Knight/White Mage and Foebreaker/Uhlan, Knight/Red Mage.