Hmm... A lot of the most common class types are covered already in some form or another.
I'd kind of like to see some sort of unarmed combat specialist class, I guess you could take the cheap FF way out and have their weapon be 'gloves' or kneeguards or something.

They'd be another lightweight melee class, lets say base 70 armour and 3 energy regen, with use of adrenaline skills like Warriors or Paragons. Rather than provide extra armour against physical or elemental damage, it would convey a moderate resistance to hex spells, lessening either their effects or their duration (not sure about that one yet, don't want to leave them open to heavy damage through something like Wastrel's Worry). The excuse there would be that they trained their mind along with their body and built up some immunity to outside interference to it, basically the usual anti-melee mesmer/necro builds would no longer be the solution 100% of the time.
They would have pretty much no spellcasting ability in their class whatsoever, but would have some defensive buffs in the form of shouts and so forth. Their primary attribute would provide inherent faster running speed and chance to block melee attacks and projectiles (including spellcasting projectiles). The interesting part would come in that their 'weapon mastery' style attribute would contain 'attack stances', with no duration time on them. These would completely alter the fighting style, effectively swapping the character to a different form of martial arts. This would effect the damage range and attack speed, as well as granting additional effects to their attacks. There could be one stance that provided a dervish-like ability to hit multiple adjacent foes at once, another with armour penetration on top of slow powerful attacks, etc. There'd be a certain mesmer-like component in that certain stances would be more or less useful against certain enemies, some suited to fighting off tanks while others for shutting down spellcasters. I suppose there would probably be some condition infliction involved. Attack skills would exist for the class too, but these attack stances would provide decent enough damage and other effects that the attack skills were an afterthought used for their special effects, rather than a necessity for damage as with most other melee classes. The attack stance in use would always be listed under their name so enemies knew what they were up against.
Attack stances would be disabled for a certain period of time after they ended, so stance-ending attacks would be very effective at crippling their offensive capabilities for a while. While they (like most other melee classes) would have one or two stance-breaking attack skills, blocking would still be an effective way of mitigating their damage in many cases. Anti-melee conditions would also be useful, such as crippling, weakness and blindness. And of course focused damage would take them down reasonably fast given their low armour for a frontline attacker.