I think that there are more then enough examples of actual martial art forms to derive a list from. A way to pick martial arts for the book could be to pick a static number you would like to apply to each class. I'm more interested in their application to current classes. Like fleshing out characters by applying "martial art x" to "y" class. An example would be a version of professional wrestling to Barbarian. Feat association begins to manifest in the players mind. I'd want that character to have a grapple feats that chain to throws. This is also an opportunity to fix player issues with the monk class by giving each associated martial art/feat progression a specific role. The following are some ideas that include previous feat progression so that entire feat lines don't have to be made per form. I have also tried to tailor them to specific classes to supplement current roles.
Barbarian: Greco-Roman, Freestyle Sambo
Feat: allows throw anything to include people with a damage modifier based on slam.
Feat: Neck Crank/Leg Lock, Adds bonus damage to grapple with a threat range and critical modifier.
Bard: Capoeira, Tai Chi
Capoeira could unlock Dazzling display without weapon focus. It could also unlock deadly stroke at BAB +8, minus the con bleed.
Tai chi could be used to enhance save checks against fear etc based on the clearness of mind. This could be an enhancement bonus to the bards various buffs for choosing this form.
Druid: Animal styles/Wild Style (generic I know)
The druid forms an affinity for specific wild creatures and tries to emulate them. At levels 1-3 magic weapon could have a bonus if cast on self. This would be to vary the usual shillelagh leveling. At 4th level and each beast shape afterward the druid can pick a favored form. When the druid cast magic fang on themselves and then wild shapes before the duration ends the magic fang applies to natural attacks of the beast shape for the duration of the beast shape. This option could be made available only if animal companion is not chosen. This could be a way to narrow the disparity in damage per round.
Fighter: Generic feat selection
Fighters should be be able to pick almost any combat feat. I don't believe fighters deserve a fighter only martial art. They will have the ability to cherry pick their favorite feats and build better feat progressions due to the fact that they are a fighter in the first place.
Monk: First and foremost,
http://paizo.com/paizo/messageboards/paizoPublishing/pathfinder/pathfinderR PG/general/whyAllTheMonkHate
The main points I took from this thread were mobility, role, and MAD. I think a simple solution would be Monk only feat progressions. I believe after the normal monk feats and APG monk styles the monk may be overloaded if you add another twenty fighting styles to their arsenal. Instead you could make the monk feats be based on personal growth of the monk and independently developing their own style. Unlocking the secret truths of martial arts as they level. Below is an example, that would also help fix the mobility argument.
mobility focused feats- Tailor feats to play off their mobility by adding special attacks that use mobility or make comparable damage to flurry.
Shadowless kick: has a damage modifier based on charge distance.
Greater shadowless kick: has a flurry built into it.
I feel like this post is drifting off topic as far as what the OP asked for. Therefor I am cutting it off here.