The weapon groups are those from the Fighter's Weapon Training Class Feature. This blog entry has a fairly complete listing.
Edit: I updated the list from the blog by adding the weapons from Adventurer's Armory 2.
Axes: bardiche, battleaxe, boarding axe, butchering axe, collapsible kumade, dwarven double waraxe, dwarven longaxe, dwarven maulaxe, dwarven waraxe, gandasa, greataxe, handaxe, heavy pick, hooked axe, hurlbat, knuckle axe, kumade, light pick, mattock, orc double axe, pata, throwing axe, and tongi
Blades, Heavy: aldori dueling sword, ankus, bastard sword, chakram, cutlass, double chicken saber, double walking stick katana, elven curve blade, estoc, falcata, falchion, flambard, great terbutje, greatsword, katana, khopesh, longsword, nine-ring broadsword, nodachi, rhoka sword, sawtooth sabre, scimitar, scythe, seven-branched sword, sharpened combat scabbard, shotel, sickle-sword, switchscythe, temple sword, terbutje, and two-bladed sword
Blades, Light: bayonet, blade boot, brass knife, butterfly sword, chakram, dagger, deer horn knife, dogslicer, drow razor, dueling dagger, gladius, hunga munga, kama, kerambit, kukri, kunai, machete, manople, pata, quadrens, rapier, sanpkhang, sea-knife, short sword, sica, sickle, spiral rapier, starknife, switchblade knife, sword cane, swordbreaker dagger, tailblade, wakizashi, and war razor
Bows: composite longbow, composite shortbow, longbow, orc hornbow, shortbow, and thorn bow
Close: armor spikes, barbazu beard, bayonet, blade boot, brass knuckles, cestus, dan bong, dwarven boulder helm, dwarven war shield, emei piercer, fighting fan, garrote, gauntlet, heavy shield, hook hand, iron brush, klar, light shield, madu, mere club, punching dagger, rope gauntlet, sap, scizore, shield spikes, spiked gauntlet, tekko-kagi, tonfa, tri-bladed katar, unarmed strike, waveblade, wooden stake, and wushu dart
Crossbows: crank crossbow (heavy), crank crossbow (light), double crossbow, gastraphetes, hand crossbow, heavy crossbow, launching crossbow, light crossbow, repeating hand crossbow, repeating hand crossbow, repeating heavy crossbow, repeating light crossbow, slaver's crossbow (heavy), slaver's crossbow (light), stonebow, tube arrow shooter, underwater light crossbow, and underwater heavy crossbow
Double Weapons: bo staff, boarding gaff, chain-hammer, chain spear, dire flail, double walking stick katana, double-chained kama, dwarven double waraxe, dwarven urgrosh, gnome battle ladder, gnome hooked hammer, halfling double sling, kusarigama, monk's spade, orc double axe, quarterstaff, taiaha, two-bladed sword, and weighted spear
Firearms: all one-handed, two-handed, and siege firearms
Flails: battle poi, bladed scarf, cat-o'-nine-tails, chain spear, dire flail, double chained kama, dwarven dorn-dergar, flail (light flail), flailpole, flickmace, flindbar, flying blade, flying talon, gnome pincher, halfling rope-shot, heavy flail, kusarigama, kyoketsu shoge, meteor hammer, morningstar, nine-section whip, nunchaku, sansetsukon, scorpion whip, spiked chain, urumi, and whip
Hammers: aklys, battle aspergillum, chain-hammer, club, combat scabbard, dwarven longhammer, dwarven maulaxe, earth breaker, gnome piston maul, greatclub, hanbo, heavy mace, knobkerrie, lantern staff, light hammer, light mace, mere club, planson, taiaha, tetsubo, wahaika, and warhammer
Kobold Tail Attachment: long lash, pounder, razored tail attachment, spiked tail attachment, and sweeper
Monk: bo staff, brass knuckles, butterfly sword, cestus, dan bong, deer horn knife, double chained kama, double chicken saber, emei piercer, fighting fan, hanbo, jutte, kama, kusarigama, kyoketsu shoge, lungchuan tamo, monk's spade, nine-ring broadsword, nine-section whip, nunchaku, quarterstaff, rope dart, sai, sanpkhang, sansetsukon, seven-branched sword, shang gou, shuriken, siangham, tiger fork, tonfa, tri-point double-edged sword, unarmed strike, urumi, and wushu dart
Natural: unarmed strike and all natural weapons, such as bite, claw, gore, tail, and wing
Polearms: bardiche, bec de corbin, bill, boarding gaff, crook, fauchard, flailpole, glaive, glaive-guisarme, gnome ripsaw glaive, guisarme, halberd, hooked lance, horsechopper, lucerne hammer, mancatcher, monk's spade, ogre hook, naginata, nodachi, ranseur, and tiger fork
Siege Weapons: ballista, bombard, catapult, corvus, firedrake, firewyrm, gallery, ram, siege tower, springal, trebuchet, and all other siege engines (see Ultimate Combat for more details)
Spears: amentum, barbed spear, boar spear, boarding pike, chain spear, doru, elven branched spear, flask pike, javelin, harpoon, injection spear, lance, longspear, orc skull ram, pilum, planson, sarissa, shortspear, sibat, spear, spear-sling, stormshaft javelin, syringe spear, tiger fork, totem spear, trident, and weighted spear
Thrown: aklys, amentum, atlatl, blowgun, bolas, boomerang, chain-hammer, chakram, club, crystal chakram, dagger, dart, deer horn knife, dire bolas, doru, dueling dagger, flask thrower, grappling hook, halfling double sling, halfling sling staff, harpoon, hunga munga, hurlbat, javelin, jolting dart, lasso, kestros, knobkerrie, kunai, light hammer, net, phaleros, poisoned sand tube, rope dart, shortspear, shrillshaft javelin, shuriken, sibat, sling, sling glove, snag net, spear, starknife, stingchuck, stormshaft javelin, syringe spear, throwing axe, throwing arrow cord, throwing shield, trident, wahaika, and wushu dart