Warmage
A 3rd Edition D&D core class, originally printed in the Miniatures Handbook but then carried over to more "general" use in the 3.5 Complete Arcane book.
The background is that unlike Wizards who spend a lot of time researching magic and collating data into dusty tomes, or Sorcerers who wield magic instinctively. The Warmage practices over and over in state sponsored military academies until the spells become almost like muscle memory for those who drill physically. They can recall spells by rote and training, rather than "feel" or "understanding".
Warmage Progression
This class behaves like a Sorcerer variant, in that it can spontaneously cast from any spell that it knows. The trade-off is that unlike a Sorcerer it's spells are selected for them and virtually all of them are direct-damage spells and there is no scope to expand that without delving into other classes.
This reliance on destructive spells is a legacy of it's original purpose in the Miniature Handbook, where classes were designed for tabletop battles to be added to units of troops, and all it really needed to do was blast opponents away at range.
They also gain armour proficiencies; being able to ignore spell failure in light armour to begin with, but gain medium proficiency at 8th level where they can also ignore failure chance.
As the Warmage progresses they learn "Sudden" Metamagic feats, which means they can just add metamagic changes to spells without upping the level of the spell. Though only one-per-day, but it's a nice enough touch if your group gets in a bind.
The class features do allow the Warmage to learn Wizard/Sorcerer spells not already on it's list, but these are restricted to the Evocation School, and pretty much just add more flashy destruction spells. In addition, the first class feature: "Warmage Edge" allows the class to add it's Intelligence bonus to the hit point damage of any spell they cast. This means that they can outstrip the destructive potential of any other spellcaster. So if your group already has a versatility caster then the Warmage becomes an excellent addition.
Making it Work
Admittedly, Warmages can do much of the things that Sorcerers can do, the main difference between them is that Warmages are much more focussed on wrecking things and are simply better at it.
Good prestige class options are those that expand the available selection of spells, giving them more versatility.
The Rainbow Warrior prestige class is particularly awesome, to the point that once you reach level 10 in the class a Warmage will make most divine casters redundant since they get to add all of the Cleric spell list to the spells available to them as a warmage, which they can cast spontaneously from their increased number of spells-per-day.