Often when I see a fix for a class it's either a houserule specific for that class or homebrew abilities for it. For example the Monk's infamous mobility and bonus attacks synergy (or rather lack therefore). Then I ask myself - "Why trying to just fix the Monk when it's really not a problem with just that one class but a problem inherent to the rules in general?" I understand that fixing one class is easier and quicker than fixing the whole system, but I think fixing the system would be more worthwhile. Let me be clear though, I don't mean fixing the entire system, because that would be way too much hard work. What I'm talking about is fixing parts of the rules that make the most problems.
Examples:
Movement rules and attack rules. The way they work, they screw over martials (Monks and TWFers in particular). To fix that I made a general houserule - feats, abilities and effects that normally function only on a full attack (TWFing feat chain, Haste bonus attack, Flurry of Blows, etc.) can be used with a standard attack. It's mostly meant to apply to things that give more attacks, but I'd rather make it more open and clarify unexpected synergies on a case-by-case basis, than make it unnecessarily restricted and complicated. It's a simple houserule and for now there was no problems with it. It made Monk a bit better, because now he can use his mobility and still benefit from his FoB. The same with TWFers. Now investing in those feats doesn't mean you have to stand still. Sure, you still lose out on your iteratives if you move, but at least you can make more than one attack.
Another problem - martials (unless specialized in crowd control or agrroing, of course) can be easily ignored by the enemies. AoOs were supposed to be scary enough for the monsters to think twice before just walking past a martial. We know they aren't. I made houserules - AoOs are essentially treated as standard attack actions. Also AoOs treat the enemy as flat-footed. Basically if an enemy doesn't pay attention to his opponent, he will be screwed.