Arbelas: Less than half a dozen illustrations but a few good descriptions. Scale or mail armour. two (short) ocrea. Enclosed Secutor style helmet with a metal crest. Armed with a gladius /dagger and crescent or semi- circular axe mounted on a fully armoured sleeve.
Could be a variant/descendant of the earlier Scissor. Probably a specialist. Fought against Retiarii and another Arbelas.
Murmillo( Myrmillo) The classic gladiator. Probably an evolution of the older 'Gaul' type gladiator when these became politically incorrect.
PLenty of illustrations. Good descriptions. Enclosed helmet with apparently either a fish- fin or even a whole fisf depicted on it. However, many illustrations show just crests or plumes. Manica on the right arm, short ocrea on the left leg. Armed with gladius and dagger. Big oval or rectangular scutum. Fought Retiarii, Hoplomachi, Thraex, Laqeuarii, Dimacheirii in short anything that moved.

Thraex ( Thracian) Again a most popular gladiator. Many good illustrations and descriptions. Enclosed helmet with- again apparently- often a Griffin style metal crest. Most often also plumes and feather crests. Long ocrea on BOTH legs, manica on right arm only. Small square parmula shield. Fought with a 'sica' a sort of curved/hooked sword( to reach behind the big shield of his regular opponent the Murmillo) or the more slender acinaces. Fought as said Murmillones but also - according to mosaics-Hoplomachi, Retiarii and Dimacheirii.
Hoplomachus. Armour almost the same as a Thraex. Two long ocrea, manica on right arm. Enclosed helmet again like a Threax or Murmillo often with additional plumes it seems. Armed with a spear and dagger. Small round parmula shield. Probably/possibly a parody on the Greek aspis shield often erroneously called 'hoplon'
Aquemanius( variant?) described as a Thraex with a spear. Could very well be a - deregatory-wordplay on Aquamanius ( wash-bassin) from the small round shield of a Hoplomachus. Or it could have meant a 'lighter' sort of Hoplomachus. See drawing below.
Provocator. Origins a bit vague. Might have been a 'guest'- type gladiator or an evolution of 'noxii' condemned criminals (soldiers?) given a last chance to redeem themselves. Or all this might just be untrue and it was simply a new class of gladiators introduced to spice up things.
Oddly enough this gladiator breaks some 'rule of thumb' rules as he has a long ocrea on his left leg and at least a medium sized rectagular or oval/oblong shield. Manica on right arm as usual and armed with a gladius and dagger. Helmets at first without a visor, later with. Almost almost never a crest but sometimes two plumes (one on either side) Best known for the cardiophylax chest armour.
Perhaps the shield is something special. It is invariablly shown without the ubiquitious big metal boss in the centre, but instead just a spine like the older Gallic shields. It just might be that this type of shield was somewhat weaker or could not be used offensively. Your guess is as good as mine. Fought other Provocators or Murmillones. This model however shows a shieldboss. But it is such a nice one I couldn't resist.

Also take a look here for some really intersting pictures of re- enactors on Flickr.The Provocator shown is really good.
http://www.flickriver.com/photos/tags/provocator/interesting/Retiarius The 'net' man Probably the best known gladiator?
Armed with a net a dagger and a fuscina trident. The left side was protected by a galerus- a heavy armoured plate fastened to the left shoulder and reaching almost to the top of the head. Under this was an armoured manica. Fought mostly against Secutors but also Murmillones and perhaps even Thraex.
Variant : Laquearius who had a lassoo instead of a net, and a spear or dagger instead of the fuscina.

This drawing comes from a Fox News site.
Secutor. Later he traditional adversary of the Retiarius. Enclosed smooth helmet with rather small eye holes so the trident couldn't penetrate. Manica on right arm, short ocrea on left leg. Rectangular or oblong shield. It seems the Retiarius was considered the 'better' of this pairing as often 1 Retiarius was paired off against 2 Secutors.

Other gladiators mentioned in texts but with few if any reliable illustrations.
Saggitarius Archer. Only illustraton shows an armoured archer with a curved -composite?- bow and an Eastern style helmet.
Cruppelarius Only illustration is of a walking tank completely encased in segmented armour and with a huge pot- like helmet.Probaly armed with a gladius and shield.
Equites Fought on horseback with spears and then with gladius and shield when dismounted. Enclosed helmet, armour unknown if any. Mostly round smallish shields.
Veles. Unarmoured light gladiator armed with spear(s)/ javelins and sometimes a shield. Almost always bareheaded. Possibly an evolution of either the Venatores or simply to mimick the Roman light infantry?
Ga(e)tulian. Only mentioned once. Light, unarmoured gladiator armed with throwing darts or small javelins.
Cathaphratarius. Heavily armoured gladiator wearing a full or 3/4 mail shirt. Secutor style helmet. Big scutum. No ocrea. Fought with gladius? or semi- spatha so might be a later type mostly popular in the East.
Gaul and Samnite. Early types of gladiators until the Gauls and Samnites became part of the Roman Empire. Later evolved into Murmillo and Hoplomachus.