I am a level 2 human warmage. I want to become a prestige class that lets me keep casting spells, but also keeps me a good, strong fighter.
Since no one else has mentioned it, how about Abjurant Champion? Full BAB, d10 per level (which could definitely help your hitpoints out), perfect casting progression, and it'll boost the
shield spell for you if you learn it via eclectic learning (which you probably should do when you can, since it'll max out at +9 shield bonus to AC while leaving your shield hand empty). [Abjurant Champion doesn't work on mage armor as written, but does work on luminous armor & greater luminous armor from Book of Exalted Deeds.]
You'd need to know one abjuration spell. This can be anything from level 0
resistance to level 1
shield to ... whatever. I don't think warmage has a single abjuration spell on its list, so you MUST learn one before you can join this class. You could learn resistance as a 1st level spell at Warmage 3, but you're probably better off learning
shield for the future AC boost or
nightshield (Spell Compendium) for a better save boost, and you can learn either as a 2nd level spell at level 6.
You also need proficiency with at least one martial weapon, BAB +5, and the Combat Casting feat. Both the martial weapon proficiency and BAB boost can be fixed by a 1-level dip into Barbarian, Fighter, Marshal, Paladin, Ranger, or a couple other perfect BAB classes who know all martial weapons. If you also take Combat Casting at level 3 or 6, you could end up entering the Abjurant Champion PrC at level 7 as a Fighter (or whatever) 1 / Warmage 6, or at level 6 as a Fighter 2 / Warmage 5. By the time you complete the PrC, your BAB would go from being +5 to +10, and you'll be the equivalent of a level 10 - 11 Warmage caster.
(You could also qualify by taking a level of Battle Sorcerer, which could give you access to your level 1 abjuration spell and exactly 1 martial weapon, but this wouldn't boost your BAB, so you'd have to be Battle Sorcerer 1 / Warmage 7 to do it, which isn't as useful as the other options.)
On top of the perfect progression and fighter BAB, the abjurant champion abilities are pretty neat. Way less useful for a warmage than, say, a sorcerer or wizard ... but you could still find use for them, especially the boosts you gain access to at level 4.
This PrC is in Complete Mage.