Ypu may set out to play a gish, but then after a while you realize that you rarely use your sword because in combat there's usually at least one spell that would be extremely useful right now to turn the situation in your party's favor.
2) There is a wizard spell 'shadowblade' that provides a nice damage that scales with level and is of psychic type. also an advantage if you are in darkness (which were always in my last two compains)
3) Shadow blade is good not only as gish but also as primary caster with great defense: light/wizard armor(~12) + Dx(~4) + Int(~4) + Shield(5) = 25 AC
Lastly, there is the hexblade-paladin, which is just... wrong.
Valor Bards can dish out some absurd damage,

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.