Hexblade and Duskblade, and not just because I like armored casters.
The Hexblade is a much better opposite to the Paladin than is Blackguard. Both the Hexblade and Paladin are warriors with secondary casting. Paladins are heavily armored, divine, pious LG types; Hexblades are lightly armored, arcane, somewhat sneaky types of sketchy alignment but not dedicated to a particular ideology. Despite the above comments, I would not consider the Hexblade underpowered. They have some superior defenses for facing high BAB opponents, including several ways to get concealment, and their main unique schtick, the curse, is a HD-based Supernatural ability, which means no SR, and the penalties are killer. Against opponents with SR, they would use their spells just for buffing; don't forget, they have full BAB. They have a nice flavor to them. I just like them.
The Duskblade is a good implementation of the full warrior, full caster concept. Not overpowered, but still strong while not completely eclipsing either the fighter or wizard. Compared to the Hexblade, the Duskblade lacks the specialized cursing ability, but makes up for it with greater offensive casting capabilities and some nice utilities (like short range teleports and such).
I like the Marshal. However, they are definitely underpowered. Giving them a specialized set of bonuses that stack with everything does not make up for being, essentially, a 3/4 BAB fighter with no bonus feats with the buffing capabilities of a much lower level bard or cleric and no healing or utilities. Honestly, kicking them up to full BAB and d10s for hit dice would probably rebalance them; they lack a fighter's bonus feats or specialized attacks of their own.