For Barbarian, I'd just take a long, hard look at the Runescarred Berserker PrC, then rewrite it into a base class. Those runescars go a long way, and the fluff is pure awesome, too! Getting rid of the more ridiculous class features like trap sense, and upping those that were overestimated by the designers like DR, is a given.
I agree on Ranger variants providing enough fuel for going up a tier. They don't need that much help. For the base class, though, expanding on the Combat Style and giving some really tangible bonuses (instead of just bonus feats usable with restrictions) when using the chosen style would be nice. Maneuvers seem like the obvious answer, but taking a page from the style-focused PrCs (Peerless Archer, Deepwood Sniper etc. for archery; Tempest etc. for TWF) and including them in the base class might also be good. Offering an equivalent of Battle Blessing for Rangers would be a nice touch where spellcasting is concerned.
Scout... needs magic, plain and simple. Most of their better class features are just the (Ex) version of stuff the casters got five levels ago. I'd try and make them partial casters of some sort, with a focus on divination and stealth-enhancing magic (they're scouts, after all), but with a few odd options mixed in, like some teleportation, and some self-buffs.
Warlock is almost good, except they simply get too few invocations, and eldritch blast gets a bit short-changed. The way it is, they lack versatility, and a little bit of power. First of all, fix blast damage progression to increase damage every odd level. How about adding on a separate progression for blast shapes and eldritch essences, like "choose one blast shape or one eldritch essence at 1st level, and at each level divisible by 3"? Then, add slightly faster maneuver progression so the Warlock ends up with, like, 15 maneuvers plus his 7 blast maneuvers.
The chassis could do with some improvement, as well. Increasing skills to 4+Int/level, and increasing HD to d8 would make me happy. These are minor tweaks, though, and don't decide a class's tier.
Rogue needs more and earlier access to rogue talents, and they need some more worthwhile rogue talents. This could be achieved by granting a martial stance (not maneuvers) progression of some kind, and upping the oomph of existing talents. Mettle, re-rolls and Abrupt Jaunt-like stuff should be the yardsticks for defensive talents. Adding more and powerful status effects with successful sneak attacks is the way to go for offensive talents. Some utility talents would be much appreciated, as well, like Hide in Plain Sight, Tremorsense/Scent/Blindsense, or at-will Identify. Also, getting rid of the sneak attack limitations would go a long way to increase the Rogue's pure power. We all love to sneak attack stuff, but roughly a third of all monsters being immune, plus mere concealment shutting it down, plus range being a problem (with a squishy chassis), PLUS needing to flank/hit flat-footed is just too much, too often.
Warmage... just needs some tweaks to the spell list, really. More utility, more actual battlefield control (for a Warmage!), more magical defense, and they're on par with the Beguiler. Improving the chassis would as always be desirable (better BAB, maybe, for a fucking WARmage...).
Hexblades are just watered-down Duskblades. You could just play a Duskblade and call it a Hexblade. But in order to provide the class with something unique AND make it stronger, I'd say get rid of the curses/day limitation and make curses inflict actual status effects (sickened, nauseated, blinded, shaken etc.). Also, why not give these guys an Improved Familiar from the get-go, and make that better over time? Should make for an interesting class.
